Nominal sizes vary
Published mattress names describe common nominal sizes. Manufacturing tolerances, regional standards, upholstery, handles, foundations, and frame construction can change the real dimensions.
Rooms are irregular
Walls may not be parallel or square. Baseboards, radiators, trim, outlets, windows, doors, slopes, and fixed furniture reduce usable space. Measure more than once and use the smallest reliable dimension.
Not professional certification
Clearance and accessibility presets are educational planning aids. They are not architectural, engineering, medical, legal, delivery, or code-compliance advice.