How to Measure a Trapezoid Bay Window Cushion
Trapezoid cushions are common in bay windows and angled window seats. They require three specific measurements: Front Width, Back Width, and Depth. Read the warnings carefully — one common measuring mistake will result in a cushion that does not fit.
Measure the depth
Measure straight from the center of the front edge to the center of the back edge. This must be a perpendicular measurement — straight across, not along the angled side.
The slanted side edges are longer than the true depth. If you measure along an angle instead of straight across, your cushion will be too deep and will not fit the seat. Always measure center front to center back in a straight line.
Measure the front width
Measure from corner to corner along the front edge of the seat — left corner to right corner. This is the longer of the two width measurements on a standard bay window seat.
Old cushions warp and stretch over time. Always measure the bare wood or frame surface you want covered, not the existing cushion sitting on top of it.
Trapezoid cushions wider than 50" may require a center seam if you select a striped fabric. Contact us before ordering if this applies to your seat.
Measure the back width
Measure from corner to corner along the back edge — the edge that sits against the wall. This is the shorter of the two width measurements. The zipper will be located along this back edge.
Choose the cushion thickness
Select a thickness between 2 and 5 inches in 1" increments. For bay window seats, 3 inches is the most common choice — enough comfort for sitting without raising the seat height too high against the window sill.
Measuring tips
If you are unsure whether your depth measurement is straight, use a carpenter's square or check that your tape runs parallel to the side walls — not along the angled edge.
A steel retractable tape stays straight across wide window seat spans. Soft tape bends along the seat surface and gives inaccurate readings on larger frames.
We produce cushions in ½" increments. Round each measurement to the nearest half-inch before entering dimensions at checkout.
Take each of the three measurements twice and compare. Bay window frames are sometimes slightly asymmetrical — if front and back widths seem unexpectedly close, measure again to confirm.
Have a complex bay window shape or an irregular trapezoid?
Email us at support@uscushion.com — send us a photo or a hand sketch and we'll confirm your measurements before you order.
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