My home SF is calculated by floorplan,whic includes all but basement..you can measure the outside footprint of home and figure it out, and double it if you have 2 equal stories

There is no national standard, but ANSI is probably used the most frequent.

http://realtytimes.com/rtcpages/20070625_squarefoot.htm

Here is a link that might be useful: ANSI Z765-2003

You basically measure it from the exterior walls. There are special rules for low ceilings (attics), knee walls (Cape Cods), etc. But generally you measure the exterior and multiply by the number of stories. Garage does not count.

Walls count, closets count, staircases count, fireplaces count, etc.

I wish I knew how our property appraiser figures it. According to my floor plan, out house is 3510 sq ft per the builder. According to my county property appraiser it's 3250. But then there are other homes in my subdivision identical to mine (floor plan) and the property appraiser shows it as 3510. There are no builder modifications or ways to increase sq ft'age in my plan.

I don't dare argue this, why make my taxes increase? Now when I had the last appraisal done, they figured the sq ft'age at 3579. They actually did measurements. Anyway, that's the figure I'm using in MLS as my house is listed.

I don't understand how you would measure it. I can measure the outside of my house, but it is very irregular with lots of angles. What do you do with the meaurements after you take them?

Forgive my ignorance, it's been many years since I took a math class.

"I don't understand how you would measure it. I can measure the outside of my house, but it is very irregular with lots of angles. What do you do with the measurements after you take them?"
Our house is like that as well. You divide the house into the various shapes necessary to cover the entire floor plan (triangles, squares, rectangles and circles) and then add up the square foot in each. Ours came out to 3797, when someone else did it they came up with 4000, pretty close considering the size. The assessor and appraiser took the lazy way out (and wrong way) and took the widest width and the longest length, and double-counted a cathedral ceilinged room, so they over estimated the square footage (they came up with around 4300).
Let's say the house is 50x34 except in one area where there is a 4x20 bumpout. You figure the square footage of the 50x34 (1700) and the square footage of the 4x20 (80) and add then together to get 1780. That's one floor. If the second floor is the same footprint (let's say it's a colonial) then you double it, to get 3560. You don't subtract for the staircase. But let's say there was a room on the first floor that went all the way up (cathedral ceiling) with no room on the second level over it, you'd subtract that square footage.
Figuring a square or a rectangle is easy. To figure other shapes you can get the formulas off the internet. Or consult your child's geometry textbook.

Every apprasier has measured my house differently. The tax records show the biggest, so that's what we used for the MLS. I think sue is right in that they divide it into shapes. I see the appraisers walking around with clipboards making drawings and a measuring tape.

outside walls definitely count. Also in bonus rooms and capes wall height over 4' is counted.

I'm glad this topic came up. Our realtor had a guy come in to draw the floor plan of the house to put on the back of the brochures. He measured the house and the sq. footage came out less than the tax rolls. We bought it as 1763 sq. ft., and have paid tax on that amount. This guy calculated it at 1729 sq. ft.

I have to say that while I'm happy with our realtors, I'm ticked this did not work out in our favour. She said she is obligated to change the sq. footage in our listing.

How do I notify the tax office about the discrepency? I'm sure we won't get any money back from paying taxes on a larger house than we have, but it would be nice.

I'm also going to have an appraiser come out to measure for a 2nd opinion. The guy calculated the numbers twice and he says they are correct, however, all the other houses in our neighbourhood of the same floorplan are aroundt eh 1760 square footage, so I'm still thinking this guy made a mistake - perhaps transposed numbers or wrote down the wrong measurements.

Is it possible the house was always 1729 but when things went computerized someone punched in the wrong last numbers? Think about it, you have someone inputting data, after a while stuff happens. I've punched in wrong numbers / letters before working on something in word or my medical data base, people are human. Unless you have old tax bills or surveys, hard to pin-point the exact year it happened.

This happened to my dad on his 2 family house. We found out when he went to sell it. We were told not to worry about it since he was paying taxes on the smaller 40 x 100 lot instead of the larger 80 x 100 lot. They said it would get fixed during the sale. I used to argue with my dad. He swore his taxes wouldn't change (higher) if we went and fixed it at the tax office. I told him it most certainly would, but since he was sick, would give up. Why would the town tax him on a 40 width, when they could make more cash on 80?

When you have the 2nd appraisal done take both to the tax office and show them. They may have to eventually look in the paper file if one exists. With my dad's house he'd saved everything since buying the house in 1967 so we were able to see where the error was entered. IIRC it was the late 90's / early 2000.

No, chances are you won't see the excess money.

Sparksals, the difference is really negligible, it's only 34 square feet. That is not a significant area at all, only about the size of a closet. I doubt that would make a difference regarding taxes.

My house has a very, very irregular footprint with 16 inner and outer corners, not all of them right angles either. Suspect the sq footage may not be precise, but I don't want to try to figure it out...

BTW, did you know that number of corners is a variable in estimating replacement cost for insurance purposes?

I thought it was heated living space. Garages, crawspace under stairs, utility rooms (not laundry) were not counted?

Rusty

Interesting thread. Recently I visited a friend in NC. Her sq footage is recorded as 3020. We went room by room, each of her rooms, bathrooms, hallways, bedrooms, living areas were all smaller than my 2700 sq foot house.(same style) My guestimate was that her sq footage was about 2000 sq feet. It certainly does change things for me when people come to my area and ask to see nothing smaller than 3000 sq feet. (Large home in my area). Now I know I can show much less than that and be ok. I'm not sure how things should be different, a measurement is a measurement, but it definitely is. When I came home, I checked some of the search sites and looked at 5000 sq foot homes in NC. They look like 3000 sq foot homes in my area. 5000 sq foot homes in my area are considered "mansions" on the tax record and they look like it".

The main person interested in square footage is the tax assessor and they do not normally have access to the interior of houses.
They use the house footprint (usually from the plat) to compute the square footage.
Adding up rooms will ALWAYS be less than this method since it ignores wall thickness (interior and exterior).
ANSI can have all the standards they want, they do not have the force of law.
They are just a 'recommendation'.
As long as the assessor uses a consistent method across all houses the taxes rolls end up being consistent.

I have never purchased a house based on square feet.
You can have all the square footage you want, but a poor layout will make the place seem small.
The converse is also true.
A house with fewer square feet but a good layout can appear larger and function better.

the reason the measurements are different is because different people have different reasons for wanting to know that information. Real estate agent and builders what to know the GLAAG- gross living area above grade. tax assessors wants to know the actual footprint which will include your garage and they want to charge you as much as they can. insurance is the same deal they want to know GLAAG or effective square footage vs overall square footage since they want to factor prices based on replacement cost for finished and unfinished space. Don't add up rooms-- there are wet walls that you can't factor into that equation...if you physically want to measure do what appraisers do- go outside and measure the house. remember if it is a cape or saltbox you don't double the first floor square footage also if your first floor layout is different from the second floor you have to facto that into the equation.