Measure the footprint and clearance
Check the full assembled or inflated size and leave room around it.
Mark the footprint on the floor
Use the published length and width or diameter to mark the area. Check clearance around the seat and allow space for any controller cable.
Check the surface and load limit
Use the surface recommended by the maker. Verify what the stated load limit covers and follow it. If the limit is missing, ask before choosing.
Measure storage as well
A deflated seat needs dry storage and time to set up. A framed seat may need assembled storage. For foam supports that sit on another surface, see the position cushion measurement guide.