This link will be of help to you, it's the NKBA rules put online. I took a quick read of your post, and Im sure you will get some good comments. You could do anywhere from 36 to 48 inches, no need to go bigger, but the larger you go, the more you lose wall space which affects possible furniture placement options, as well as cabinet plans. So think about how you want to furnish the rooms, and how you want your cabinet layout to go, how much counter and storage you need, placement of appliances - that is key. Now you could go down to as little as 36 inches, but I would consider 40-42.

Were there any architectural features you removed from that wall?

Agree with BC Jones, 40-42 inches seems good. It's nice to have a kitchen entrance wide enough for two people to pass through at the same time. But I would leave the wall beside your fridge deeper than 28" (plus trim). Fridge dimensions vary so much. You might want to leave a little room for a deeper model in the future.

I did the same in my 30s Tudor house. Original opening was a 30 inch door in the corner of the kitchen. My house has several arched openings including a 48 inch wide archway from foyer into living room. We actually traced the existing opening to match the arch shape. From the kitchen side, we ended up with about 5 inches of wall past the countertop on one side and the fridge on the other. We have a counter depth one so that won't change much with a different fridge.

Most people won't catch the change but a true old house lover knows that kitchens of that era had doors.

Do you have any other cased openings to match the width and trim profile?

@Lyndee - here at two pictures (again not great). One is the dining room to living room entryway (65”) and the other is the living room to foyer (60”). One concern of mine is that the smaller the entryway, the more out of place it may appear. I would ideally mirror the 65” one but the max I can do is about 50”.

To that end, Bc Jones & Mccarroll - thank you a ton for the thoughts and considerations. I’m a little concerned 40” would be too small, i.e., what was the point in “opening things up” for an entryway that size. That being said, if you think that is plenty of space by conventional standards, I welcome your continued thoughts.

@cpartist - what do you mean by architectural features? There is a coved ceiling on the dining room side, but I think I will be able to preserve that. The wall itself is load bearing, so I will need to accommodate for that.

I think it will look fine at anywhere between 40 to 50 inches wide, as long as you get the height and trim exactly matching the opening on the adjacent wall.  If the openings weren't so close you could get away with almost the same profile trim,  but you are going to need the two sets to match.  I can't distinguish the detail but some of those are vertical butted against horizontal and only the outer trim is mitered.

Honestly I don't have enough personal experience to tell you the optimal size. I've got 2 30" doorways into my kitchen--those are unpleasantly tight when entertaining. Another 10" there would make a big difference. And then we have a 48" patio door, and that is great. I think the crucial point is the one BC Jones made--are you losing useful wall (for cabinets, or for living room furniture placement)? If not, go big.

Posting a plan of the kitchen and adjacent space with all dimensions will gain you the best advice.

This isn't perfect, but here's a floor plan I just drew up. The kitchen should be about exact, the other rooms are estimates but should be close. This is the upper unit of a duplex, so the lower right foyer leads to a staircase. The kitchen cabinets/etc. aren't exact but close - built in cabinets (original to house) on lower right, standalone fridge on top right, and brand new wall of cabinets on the left.

FWIW the original entryway to the kitchen was from the hallway, but I am closing that doorway to get a longer run of cabinets. I will lose a wall in the dining room but didn't have much plans for that space anyhow.

My kitchen is 9'9" x 11'9" so very similar size to yours. It is an awkward width as too narrow for an island and rather wide for a galley. I would rethink your plan to try to squeeze in some additional counterspace. Does your builtin have usable counter space or just storage? 

My kitchen has fridge, sink and dishwasher one side and cabinets and stove on the other side. We pulled the cabinets forward 5 1/2 inches and used a slide in stove for extra countertop depth. It might not seem like much but it is enough space to store all the countertop items behind the stove and at the back of the counter so they don't get in the way. I would want a small amount of counter space beside the fridge for landing area when storing or retrieving fridge items. Unless you are super organized and never need to move items around to fit the latest addition, you need space on the same wall. Try to put something on the counter, turn and walk five feet to open fridge door. Then walk back for your item and carry it across the kitchen  and hope the fridge door didn't shut while you were getting the container. Plus, while you are doing that, no one can enter or exit the kitchen without bumping into you.

My kitchen is 9'9" x 11'9" so very similar size to yours. It is an awkward width as too narrow for an island and rather wide for a galley. I would rethink your plan to try to squeeze in some additional counterspace. Does your builtin have usable counter space or just storage? 

My kitchen has fridge, sink and dishwasher one side and cabinets and stove on the other side. We pulled the cabinets forward 5 1/2 inches and used a slide in stove for extra countertop depth. It might not seem like much but it is enough space to store all the countertop items behind the stove and at the back of the counter so they don't get in the way. I would want a small amount of counter space beside the fridge for landing area when storing or retrieving fridge items. Unless you are super organized and never need to move items around to fit the latest addition, you need space on the same wall. Try to put something on the counter, turn and walk five feet to open fridge door. Then walk back for your item and carry it across the kitchen  and hope the fridge door didn't shut while you were getting the container. Plus, while you are doing that, no one can enter or exit the kitchen without bumping into you.

My kitchen is 9'9" x 11'9" so very similar size to yours. It is an awkward width as too narrow for an island and rather wide for a galley. I would rethink your plan to try to squeeze in some additional counterspace. Does your builtin have usable counter space or just storage? 

My kitchen has fridge, sink and dishwasher one side and cabinets and stove on the other side. We pulled the cabinets forward 5 1/2 inches and used a slide in stove for extra countertop depth. It might not seem like much but it is enough space to store all the countertop items behind the stove and at the back of the counter so they don't get in the way. I would want a small amount of counter space beside the fridge for landing area when storing or retrieving fridge items. Unless you are super organized and never need to move items around to fit the latest addition, you need space on the same wall. Try to put something on the counter, turn and walk five feet to open fridge door. Then walk back for your item and carry it across the kitchen  and hope the fridge door didn't shut while you were getting the container. Plus, while you are doing that, no one can enter or exit the kitchen without bumping into you.

My kitchen is 9'9" x 11'9" so very similar size to yours. It is an awkward width as too narrow for an island and rather wide for a galley. I would rethink your plan to try to squeeze in some additional counterspace. Does your builtin have usable counter space or just storage? 

My kitchen has fridge, sink and dishwasher one side and cabinets and stove on the other side. We pulled the cabinets forward 5 1/2 inches and used a slide in stove for extra countertop depth. It might not seem like much but it is enough space to store all the countertop items behind the stove and at the back of the counter so they don't get in the way. I would want a small amount of counter space beside the fridge for landing area when storing or retrieving fridge items. Unless you are super organized and never need to move items around to fit the latest addition, you need space on the same wall. Try to put something on the counter, turn and walk five feet to open fridge door. Then walk back for your item and carry it across the kitchen  and hope the fridge door didn't shut while you were getting the container. Plus, while you are doing that, no one can enter or exit the kitchen without bumping into you.

The plan says it all…. Go ahead and widen it as much as possible (especially since you are loosing the opening from the hall)

I would probably build in a little more depth for the refrigerator so you don't end up with one hanging out at the doorway if you end up getting a deeper one in the future. Unless you are committed to always buying true counter-depth or a built-in. (These are always my preference but budgets and availability change over time)

Lyndee Lee, the built ins do have counter space. Here they are in all their glory mid-renovation 😅 they’re a bit shabby, but will nice when they are cleaned up. Ideally, the fridge would be right next to counters, but I think this will be manageable.

On the fridge side, to its left as you stand there facing it - what were you going to do with that space? Tall pantry, 24 inch deep, is what I think would be the best option. Otherwise on a quick look you did a good job giving yourself ample counterspace. If you haven't already done your kitchen 101 on Houzz, not much more I can say, other than: use as many drawers as possible for your lower cabinets. Re: your opening: so it seems clear that you could go from a 3 foot wall on either side of the opening to somewhat less - depending on how much of the counter you want to be visible from the other room. I think you could safely go from 3 feet to 2ft 6 inches, but without putting this into design software, I can't judge how it would look to go less than 2.5 feet. Assume that the one key goal of the opening is to get more natural light into the new room.

BC, to your comment on the pantry/fridge space - if you look in the photo of my built-ins, you will be able to slightly see a pantry cabinet to the left that extends to the ceiling. It's not massive, but useful. My concern with putting new cabinets around the fridge is that it will look a bit odd having the original built-ins right next to new cabinets (otherwise, more pantry space, the better for sure). Thus, I have kept it new cabinets on one side, and old/built-ins on the other. The stove/fridge were originally on opposite sides of the room, but I figured having the fridge adjacent to counter space is more useful than the fridge being immediately next to counters.

What you also can't see is that to the right of the built-ins is a large window (you can see in the first picture in the thread). The opening will bring natural light in from both sides. The biggest motivation for the new opening was (1) better use of kitchen space (longer run of counter on the new side) and (2) somewhat open concept, but not full out blowing-out-the-wall type open.

I really appreciate everyone's comments. I am probably leaning towards the 44" - 48" range for the opening, with the main factor being if I ever choose to have a larger fridge. That being said, I plan on living here for 5 years +/- and renting it out afterwards (part of a duplex I bought), so I may not be around for another round of appliances later on.