I will look for the answer to this question too! Our current plans have ours drawn at 36x72. I am wondering if I should go to 42x72. It would require taking some space from our office and I am not sure it is worth it for a room that is not used too much.

Found this interesting article.....

The Guest Powder Room
(Part 1: Design Phase)
No other room in the house is seen by guests more often, with the possible exception of the kitchen.
It should come as no surprise then, that the powder room is remodeled and upgraded more often than any other room in the house.
Because of its smaller size, the powder room is the easiest room for the homeowner to experiment with their style, and still make a big statement with a relatively low budget.
Today, the powder room is no longer just about function and picking out a basic sink and toilet. The design possibilities are limited only by your imagination, or that of your designer.
The Guest Powder Room is a formal room, reserved for the exclusive use of guests. Family members will have their own half bath or WC to use.
Whenever possible, the Guest Powder Room should be placed somewhere near the front door. It should be situated so that guests do not have to walk into private areas of the house. The front hallway is preferred over the family room or bedroom area of the house.
The Floorplan:
When planning a new guest powder room make sure your plan accomodates all those who will use it, including guests of all ages.
While the average powder room today is 20 sq.ft (4'x5'), the trend is toward bigger, more spacious rooms.
Diminutive bathrooms are not accessible to those in wheel chairs ... and are difficult for those using walkers or crutches, those with leg or arm casts, or those who require assistance in the bathroom (including small children).

Accessible powder rooms must be at least 5' x 5' and are more usable if a pedestal or wall-mounted sink is installed, rather than a vanity with base cabinet.
Planning your bath requires more than just choosing the look you want, or selecting fixtures.
Bathrooms, no matter how small, require piping behind the walls and under the floor. Fixtures once in place, cannot be moved without tearing up walls and floors.
Because the toilet is permanent, its placement should be the first consideration when planning the bathroom.
Typically, the plumbing and fixtures in any bathroom are placed along a single wall. This reduces plumbing costs, but may not necessarily provide the best arrangement.
Believe it or not, increasing the space between and/or in front of fixtures, or by moving a doorway only a few millimeters, can mean the difference between discomfort and ease of use.
Below are four different floor plans for a 5'6"x6'6" guest powder room with a window.
Adding one or two feet to the length of the room greatly increases both accessibility and functionality, as the following illustrations demonstrate.
GRAB BARS / SAFETY RAILS:
When designing your bath, be sure to include grab bars/safety rails to the side of the toilet.
Grab bars and rails installed near the bathroom toilet will help avoid injury by providing safety, additional support and balance when sitting, standing, transferring from a wheelchair or walker; or using crutches.
Grab bars/safety rails must be made of heavy duty steel, and must be anchored to the wall studs to guarantee safety and support. At no time should towel bars be used as grab bars. They cannot support the weight of a falling adult.
Don't like the stark, stainless steel, institutional look? Current models are available in a variety of finishes, and blend well almost any decor.
DOORWAYS:
All doorways should allow at least 32" for easy access.
If quarters are tight, a door that swings outward into a hallway or adjoining room allows the necessary space to turn around in the bathroom without first closing the door. Verify that there is enough clearance for the door to open completely, especially in hallways.
Pocket doors (doors that slide into the wall) allow full access without taking up clearance room for the swing. However, they can be difficult to use, especially for children and the elderly.
If the door opens into the room, consider a wall-hung sink or pedestal lavatory instead of a vanity cabinet if it is close to the door. When left open, vanity drawers and/or doors will interfere with the bathroom door resulting in damage to the bathroom door and/or vanity. In addition, such an arrangement can create a safety hazard.

WALL HEIGHT:
Wall height needs to be considered only if it differs substantially from the norm, as is the case with sloped ceilings.
A height of at least 80" is required for standing, with at least 24" of floor space in front of the toilet or sink to maneuver around.
If there is not enough ceiling height when the toilet or sink is placed on the short wall, consider boxing in the area behind it. This will move the toilet or sink forward to allow for the needed head room, and provide additional shelf and/or storage space.
The soil stack need not be placed behind the toilet itself, it may be in an adjacent wall. But there must be enough room beneath the floor to accommodate the horizontal pipe slope.
STORAGE:
There should be a place to store hand towels, toilet paper, soap, paper cups, etc.
Resist the temptation to store/use toothbrushes, hair dryers and other family items in the Guest Powder Room.
Console tables, bath furniture, and custom vanity cabinets are all possibilities.
If a pedestal basin is used, a recessed compartment, narrow closet, or medicine cabinet with a mirrored door is a good choice for most items.
To prevent damage to a china pedestal lavatory, avoid placing loose objects on shelves above the sink.
LIGHTING/ELECTRICAL:
Ideally, there should be at least 10% natural light in a bathroom. Where it is impossible to add a skylight, window, or glass block wall, adequate artificial lighting is critical.
Avoid placing a single light fixture in the middle of the room. Instead, consider recessed spot lighting which is both visually appealing and has a low profile that's perfect for a small space. Adding wall sconces near the mirror will help eliminate harsh shadows.
There will be times when an electrical outlet will be needed. Install an electrical outlet near the sink.
VENTILATION:
Even though moisture and condensation are generally not a concern in a powder room, adequate ventilation is important. Sounds seem louder in a small room, so choose an exhaust fan with the lowest sone rating.

The Guest Powder Room ...
(Part 2: The Fixtures)
When designing a bathroom, there are certain limitations that must be dealt with, primarily ... the fixtures.
When all is said and done, a toilet maybe a toilet and a sink a sink ... but that doesn't mean you have to confine yourself to conventional bathroom fixtures.
For instance, a bronzed bath creation from Landmark Metals like the one shown at the right, can turn manor house dreams into reality. (and yes, the inside of the toilet is white vitreous china)
Toilets
Flush technology has come a long way since the days of the pull chain. But the latest and greatest might not be right for you.
Any toilet with the words "pressure assist" or .. "power" in the name or description, tend to be extremely loud when flushed.
The noise level could intimidate unsuspecting guests, and can be disturbing to others in the house if used frequently as when a party in progress. When in doubt, TRY BEFORE YOU BUY.

HEIGHT
Toilets come in a variety of heights from 10" to 18" (measured from the bottom to the top of the rim, not including the seat).
The standard toilet is 14 1/2" - 15" high, which most people find too low to be comfortable.
In order to meet the standards of the Americans With Disabilities Act, toilets should have a height of either 16 1/2 inches (used in residential construction) or 18 inches (used in commercial construction).
This is comparable to the height of an average household chair - just over 17 inches - making it easier to sit down without falling, and stand up without putting stress on the knees.
While these units were designed to allow easier access to the facility for disabled people, those without disabilities often prefer them to traditional units. This height is becoming increasingly popular for use in the Master Bath, but should definitely be considered a standard for use in the Guest Powder Room.
Individuals under 5ft. 2in. tall will find that their feet dangle in mid-air when sitting on an ADA compliant toilet. A small movable platform, step or stool - 10" deep and no higher than 2" - 3" will offer a place to rest the feet while sitting and should take care of the problem for those shorter individuals.
WALL or FLOOR MOUNT
Standard toilets mount to the floor and have a short pedestal base below the bowl. They adapt well to almost any type of decor.
Wall-mount toilet bowls are fastened to the wall, do not have a pedestal, and can be set at almost any height. While they can be used in almost any type of decor, they are most often used in a contemporary or Euro-style setting.
SHAPE/SIZE:
Toilets come in round-front and elongated sizes, with many different shapes and styles to choose from.
Round-front toilets are 2" shorter than elongated models, and are popular where space is at a premium or where a more traditional look is preferred.
Elongated toilets are the best choice for most homes. The extra space in the front makes it easier for males to use.
The style you select is a matter of personal taste, and you can choose from a variety of styles, ranging from contemporary to traditional.
COLOR/PATTERN:
Toilets come in more colors than just white, but most people prefer white because they consider it the easiest to decorate around and less likely to go out of style.
Manufacturers offer toilets in range of colors from white to black. Although most color choices are in the lighter, neutral, end of the spectrum. The actual number of available colors varies by manufacturer.
Black is another popular fixture color in the powder room. When gold colored accessories are paired with black, the result is truly dramatic.
If you want color, but think the pastel shades are too "quiet" and black a bit daunting, consider one of the new Artist Edition, hand-painted fixtures from KohlerMany of the Artist Edition patterns include sink/vessel bowls, pedestal lavatories, toilets, bidets, coordinating ceramic faucet trim, tile and accessories to complete the picture perfect setting.

TANKLESS
Most residential tankless toilets are actually stylish wall-mount toilets with the tank hidden within the wall itself.
An example is the Tessera by Geberit. These units provide a sleek, clean look without resorting to smaller fixtures or sacrificing design options.
Since the toilet tank (cistern) is built into the wall, an additional 6" to 9" of floor space can be gained (depending on the bowl shaped selected).
The flush actuator is generally mounted above the bowl but some manufacturers, such as Geberit, offer a remote unit that can be placed on the wall within 6' of the tank.
New flush technologies that use a pump instead of a water tank, have not only created a true tankless toilet, but have allowed manufacturers to actually rethink the shape of the toilet.
For instance, Kohler's brand new Purist Hatbox electric toilet offers a clean aesthetic both visually and physically with its innovative tankless design.
The advantage to the new breed of electric, tankless toilets is that they offer a powerful flush that is much quieter than conventional power models.
The disadvantage of course, is that they cannot be flushed if the electric is out. Definitely not a good choice for a main bathroom or if it's the only toilet in the house.
Sinks/Lavatories:
When choosing a sink for the guest powder room, keep in mind that this is a room intended for use by a single person. A double bowl sink is used when a bath is to be used by more than one person at a time. The guest powder room should have an elegant single bowl sink.
Excellent choices for use in the guest powder room include pedestal lavatories, vessels, console tables, self-rimming sinks on marble countertops, and furniture-quality vanities.
Modular vanities, those that are made by kitchen cabinet manufacturers, tend to look out of place in the formal setting of the guest powder room.
Here, practicality is less important than appearance ... and the trend is the look of fine furniture rather than utilitarian boxes. American furniture manufacturers are now making furniture specifically for use as high-end vanities.
If you prefer antiques or the distinctive look of Old World furnishings, custom bath furniture is the perfect choice. One-of-a-kind vanities can be had by converting small antique dresser cabinets and drawers.
Pedestal lavatories and vessel sinks are the perfect choice for the powder room. However, you must make this decision before construction begins, because the wall-mounted faucet pipes must be roughed in before the drywall is installed.
Pedestal lavatories/bathroom sinks feature a basin (bowl) that is positioned at a comfortable standing height and rests on a pedestal base that conceals the drain and supply lines.
Pedestal sinks are available in styles ranging from contemporary to Victorian. In a large bathroom, they create a focal point. In a small bath, their slim profile visually enlarges the space.
These lavatories are most often made from vitreous china, but can be found in porcelain coated steel. For a truly custom lavatory, these sinks can be bronzed.
The most elegant form of bathroom sink today is the Vessel.
Vessels are reminiscent of china washbasins and are finished inside and out. Vessels can be installed to rest above the countertop. Some can be installed with a wall-mount bracket.
Spun Glass and Cast Iron Vessels can also be installed in a self-rimming application. If you choose a glass vessel, look for tempered or laminated glass. Plain glass will shatter on impact.
Also note that glass shows water spots and fingerprints, which is particularly noticeable on these exposed bowls.
A console table offers a unique alternative to a pedestal or counter top lavatory.
Unlike pedestal lavatories, where the lavatory and matching pedestal are purchased together as a unit, console tables are sold in a variety of configurations, which allows for a complete custom look.
Console tables feature tops of marble, vitreous china, blended stone or fireclay which offer ample countertop surface for displaying toiletries. Marble, vitreous china and blended stone countertops are pre-cut to accommodate undercounter lavatories, such as Kohler's Artist Editions decorated lavatories shown at the right, and widespread faucets.
Lavatories/bathroom sinks are designed for use with vanities and counters.
They are available in Self-rimming, Tile-in, Undercounter and Vanity Top models. Your choice will be determined by your personal preference and particular installation.
Faucets:
Faucets display an almost infinite variety of styles and finishes.
Some hand painted fixtures offer matching faucets. Some faucet manufacturers produce faucets with interchangeable Handles, Handle Insets and Skirts that can be changed at anytime for a different look.
Very few vessels have pre-drilled holes for faucets. Deck-mounted faucets for vessel sinks must be extremely tall to clear the bowl. Stylish wall mounted faucets are the best choice.
The Guest Powder Room ...
(Part 3 Decorating)

When it comes to guest powder rooms some say it's all about Breaking the Rules
Even if the rest of the home is done in a traditional style, this is the one room in the house that actually stands alone when decorating.
Give the room a personality of its own, whether dramatic, sophisticated, whimsical, or romantic. Experiment with colors, textures, fabrics and unexpected embellishments.
Color/Texture/Pattern:
Whatever the reason, powder rooms seem to be the only room in the house where all the rules about color simply do not apply!
The small, intimate nature of the space and its public role to receive guests, actually invites the use of patterns one wouldn't dare use in a larger room.
Dark, bold colors work well here, making the room appear rich and dramatic rather than the expected claustrophobic box. Stark contrasts actually liven the room without jarring the senses!
On the other hand, using all white, especially in a windowless room, will tend to make the room look dreary, rather than airy and bright.
About the only color rule that does seem to work, is the use of color schemes that are pale and cool. Pastel tones in blues and greens, neutrals, and whites add to the feeling of calm and space.
Accent colors, a few small splashes of bright, light colors, mixed with liberal amounts of white will keep the room from feeling dreary. But remember, too many colors in a confined space can be confusing to the eye.
Floors:
A dark, or "warm" colored floor will absorb the light and visually raise the floor. Depending on the material used, this can have the effect of making the room feel small and cramped.
On the other hand, a light colored floor will help evenly diffuse light, adding a lighter and brighter touch to the room. Light colored floors are also easier to keep clean, because you can see the dirt. Again, the choice is a matter of personal preference.
As with any room where water is present, floors should be slip resistant and made of materials appropriate to wet areas.
Pictures in magazines, including the one at the top of this page, often showcase bathrooms with what appears to be wood flooring.
You should know that these photos are provided by the manufacturers of bathroom fixtures, and are designed to sell bathroom fixtures.
Photographers choose "wood" because it makes the photo set appear more home-like and less clinical or institutional ... not because it is a practical (or even desirable) flooring material.
A Note About Hardwood:
Hardwood and bathrooms don't mix.
No matter how well sealed the wood, continued exposure to moisture will eventually ruin the floor - even in a seldom used powder room.
Installing a wood floor in a bathroom generally voids the Mfg's warranty.
Ceilings:
Light colors are usually most pleasing for a ceiling, because ceilings are seen in shadow. Painting the ceiling one or two shades lighter than the wall color will unify the space and help reduce the "boxed in" feeling. You can buy separate paint for the ceiling, or mix your own by diluting the wall paint with white paint in a ratio of 25% color to 75% white.
If the ceiling height is over 8', painting the ceiling a darker shade than the walls will visually lower it, and give the room more of a cozy feeling. However, if the color is very dark, the ceiling will appear to push up and disappear when the lights are turned on at night. Lowering the ceiling will give the room a more balanced look.
Walls:
Avoid covering the wall with vertical lines (stripes or patterns). They add height to a room, but reduce visual space. Horizontal lines make a room seem more spacious.
A chair rail, border of tile or wall paper, or wainscoting capped by a strong horizontal band with plaster or wallpaper above combined with a baseboard and sometimes a crown molding at the ceiling adds horizontal lines that visually enlarge the perimeter of the room.
Wallpaper can open up a room and make it appear bigger. Patterns and designs with lots of white space, small florals, sky, cloud and shell patterns will help expand the walls.
Wall murals that create a distant horizon, designed to help expand the space visually, work very well in a powder room.
Mirrors/Art Work:
Mirrors expand space in every direction, making the room appear larger. If the only logical place to put a mirror is opposite the toilet, place it high enough that is does not reflect the toilet itself.
If there is no window in the room, a painting or photograph reflected in the mirror can give the room depth.
If the room has a window, position the mirror so the sunlight doesn't hit the surface directly or create glare.
Ideally mirrors over the sink should be illuminated by a series of small lamps around the entire perimeter; or at very least, a row of lamps at both sides.
Accessories:
In addition to towel bars, soap dishes, etc., plants and flowers are a great addition to powder rooms. Plants need natural light. If you don't have a window, use silk plants and flowers. Not only do they look great all the time, they never turn brown!
Avoid placing heavy or frequently used objects over the toilet bowl.
Procelain is breakable. A falling jar or object may chip or crack the toilet.

Oops! All those foot symbols (') in my previous post should have been inches (") - sorry! Don't know what came over me.

Our current powder room is 3 feet wide and it is not big but adequate. I think it is 6 feet long. 3x6 would be the minimum I would want for a powder room.

The powder room in my house is 42" X 88". The pedestal sink is at one end, and the elongated toilet is at the opposite end. The door is in the middle of one of the long walls, with a floor-mounted door stop to prevent the inward opening door from colliding with the front of the toilet. There is also a window directly above the toilet (opposite from the mirror above the sink), which helps to prevent the space from feeling claustrophobic. I don't think I'd want to go much smaller, or there wouldn't be room for an inward opening door.

We had a 40" by 72" powder room where we used to live. It felt plenty roomy in width, but the first change I made was to cut loose the door-frame and turn it around to make the inward swinging door into an outward swinging one. To heck with tradition, it made sense to change. If a large friend wanted to use the powder room, the inward swinging door would hit the toilet before it was all the way open, which meant they had to really push up to (or sit on) the vanity to close the door behind them.

Thanks for the information! I think we'll make the powder room 3ft by 6ft with a pocket door and a compact elongated toilet.

We'll try to make the master more accessible for disabilities for future in-law use since it also is on the main floor. But that will be a later project. It's a simple three-part bath right now and will stay that way until I win the lottery :)

I added a powder room to our main floor. I think the measurements are 6'6" x 36". I put a Toto Ultramax toilet at one end, and put a wall mounted vanity (shown below) at the other end, and I had to flip the existing door from inswing to outswing. The wall mounted vanity and the large mirror above help to make the room not seem cramped.

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Bob: That vanity looks great. I love the idea of a wall-mount sink. I've even considered wall-mount handles for the sink.

Bert

Bert76, wall mount handles/spigot would be fantastic. We bought the Porcher ELFE sink, single hole drilling, and that is off to the side of the tiny sink, not centered behind it. If I had only planned for the wall mounted setup.......

But our little 3/4 bath is has a 40x40 shower at one end, and the rest of the room has this tiny flat sink in front of the pocket door in the center, then the American Standard Cadet 3 Compact Water Sense toilet to the other end. The toilet/sink width is 30 inches, and 6 feet long. It would have been all 40 inches wide like the shower, but while I was gone the contractor decided to reduce the room width, avoiding the remodel of a closet doorway in the adjacent bedroom. I would have voted for taking the space from the closet, hang the extra work, but work was moving right along when I returned homme.

Also, the pocket door POCKET takes a bit more space than a flat wall does. I have looked into what I call a BARN DOOR, with a surface mounted door sliding sideways if there is some extra wall space. This works pretty well in ultra modern surroundings, and it can be very decorative hardware. Also, if there is no window in the powder room, you could insert some high panes in the door for some natural light borrowed from adjacent rooms.

My WOW factor with this tiny bath is the ornamental oval mirror above the tiny sink. The pocket door is usually in its pocket, and the view into the powder room is the mirror and the Elfe sink.