I'm about to put windows in a deer blind I'm building for my son and grandkids and I can't remember the height of the windows in the stand that a sold a few years ago. It's a ground blind that will be 2 ft off the ground. The hunters will be 5' 6" to 6' 1" and I thought 36" might work but it seems too low.

What you are sitting on matters. The best thing is to figure it out using whatever it is the shooter is going to be sitting on. And remember, kids grow up quick, although you might have a long line of kids in mind?

The only way I've found is to test it.

Set up a reasonable facsimile of the shooting situation: what's the kid going to be sitting on? What's he going to be wearing? Make it as accurate as possible. Then set up a crossbar arrangement and have the kid mount the rifle. When it looks about right, measure it with a tape rule and go for it.

I built my last tower blind with adjustable shooting rails. As the grandkid gets older, I can raise it by just changing 2 screws.

^^^
Same idea as mine, but shaman explained it much better!

The last one I built I put the windows at 40”, but it also depends upon the height of your chair.

Same here.
And we have height adjustable office chairs in all the blinds.

Also bear in mind whether you are looking down, looking straight out at a rise/hill, or looking up a hill. The 40” recommendation is a good start. It CAN be a bit high if looking down a hill or at a feeder that is really close (25-50 yards). Also may be a little high if small kids will be hunting it..

Set in a chair, measure from floor to your eyes, make that the center of your windows.

Thanks but that wouldn't work me because the bottom of the window would be 44"above the floor. The the seat in the office chairs I'll be using can be adjusted from 15" to 19" above the floor but even with the seat all way up 44" hits me about chin level. Looking through a scoped rifle on my kitchen countertop (36") with the seat all the way down it's too low but 38" seems just right. I should have done that first.

I have 22 box blinds on my club and they are all 38 in with carpet on the 2x4.

Probably built over a 100. 40” has always worked. Few midgets simply stood up to shoot.

36-38 will work.

When sitting it works good.

How close do you think they will get?
That is your low point.