The above is good advice IF you are shooting level or fairly level. Average height 38" to 40 from floor. But then young or older person wants lower. Also tower blind may need to be lot lower for downward shots or higher for uphill shots. Some add flat 1 x 6 at window level to raise and steady the gun barrel. Then I'm crazy enough and make my blinds out of privacy fencing and window will have stair step hole, one slat 38', next one 39, and next 40". Have various terrain and various ages of family using em. Then you can also have an adjustable chair.