Inset Chair Seat Sizing?

[Sean Moore]

Im working on a set of 6 dining chairs that will have an upholstered seat cushion inset into an 18x18" opening.

How much smaller should the plywood seat be to accomodate for foam and upholstery? Im thinking 1/8" on all sides, but I also dont want to leave a noticeable gap between the seat and the frame.

[Jamie Buxton]

The padding and cloth will wrap around the edges of the plywood, right? Figure out the thickness of the padding and cloth, and that tells you the dimensions of the plywood.

[Jim Becker]

I agree with Jamie...this is, more or less, a math problem. You need the material to determine that. Personally, I'd get a little extra material so you can use some to make a test piece to determine just how much the seat base "grows" when you secure the padding, liner and upholstery material across it at the intended "tension". Measure the bare sample seat pan before applying the materials and re-measure after to see exactly what your allowance needs to be.