In Wisconsin they now have a building code that requires at least 36". 40" is a very good size. It is hard to visualize on the floor if you are just laying it out. I would grab a sawhorse and a piece of plywood to get the height of a counter and then see if you think 40" is still too narrow. A few inches can make all the difference!

Hello,
The NKBA recommends the work aisle for one cook should be 42", and if you have the room 48" for multiple cooks. I usually keep it close to 42" when designing kitchens. In your case, if it feels too tight then increase it, you have to live in the space and work comfortably. Hope this helps.

I agree with Cindy Kelly kitchen design. I also like to leave at least 42" between and if you can add a little more, even better. 48" is ideal if you have the space.