Measure the chair’s usable seat area side-to-side and front-to-back with a rigid tape, not the outside frame, and match those numbers to the cushion maker’s listed dimensions.
A cushion an inch too wide hangs over the arms and slides; one an inch short leaves a gap you feel all day. Tags rarely match the chair because most makers list cushion size, not seat size — so the tape measure decides, and it takes about two minutes.
You’ll need a rigid tape (a soft tailor’s tape sags across a wide seat and reads short), a pencil, and paper or your phone.
Where to Measure: Width, Depth, and Thickness
Take all three on the seat itself, not the outer frame.
- Width: side to side across the front of the seating area, between the arms. On an armless chair, measure edge to edge at the widest point.
- Depth: front edge of the seat to where it meets the backrest. On an existing cushion, use the longest front-to-back measurement.
- Thickness: for a replacement, measure the old cushion top to bottom. For a chair with a back cushion, measure from the top of the chair down to the seat-back junction.
Write each number down and label it. Mixing up width and depth is the most common sizing error — and the one that sends a cushion back.
Polywood’s cushion sizing page defines depth as the longest front-to-back measurement and width as the widest left-to-right measurement. Cushion.com’s guide puts it plainly: measure the chair, not the label.
Special Cases: Back Cushions, One-Piece Seats, and Odd Shapes
Curved, tapered, and multi-part cushions need extra measurements, because one top-edge reading won’t capture the shape.
A separate back cushion takes two numbers: back width side to side, and back height from the seat-back junction to the top of the back area. Subtract the seat cushion’s thickness from the chair’s total back height so the back cushion doesn’t push the seat cushion forward.
A one-piece chair cushion ties seat and back together. Measure seat width, seat depth, and the chair’s back height, then add seat depth to back height for the total length. Cushion.com recommends adding 1 inch to width and depth for fit and comfort.
A bench cushion needs the full usable width and front-to-back depth, plus the same 1-inch allowance.
Deep seating, chaise, and sectional cushions get measured in two passes — seat section first, then the backrest on its own. Pull the fabric taut; a slack cover reads longer than it is.
Rounded or tapered cushions get each side measured at its broadest point. Don’t rely on a single top-edge measurement when the shape narrows toward the back.
| Cushion Type | What to Measure | Allowance |
|---|---|---|
| Standard seat cushion | Usable width between arms, seat depth | Compare to maker’s listed size |
| Separate back cushion | Back width, back height minus seat thickness | Check clearance after install |
| One-piece seat-and-back | Seat width, seat depth, back height (sum depth + back height) | Add 1 inch to width and depth |
| Bench cushion | Full usable width, front-to-back depth | Add 1 inch |
| Deep seating or chaise | Seat section, then backrest section | Pull fabric taut first |
| Rounded or tapered | Each side at its widest point | Use broadest readings |
| Armless chair | Edge to edge at the widest point | Compare to listed size |
Match your numbers against the maker’s spec sheet rather than guessing a “standard” size. For desk setups, our roundup of tested work chair cushions lists the measured seat range each one covers.
Fit Mistakes That Send Cushions Back
Almost every bad fit traces to one of five slips — all avoidable before you order.
- Measuring the outside width of the chair instead of the usable space between the arms, producing an overly wide cushion that bunches at the sides.
- Measuring only the front edge on a tapered or rounded seat, missing the geometry that decides the fit.
- Measuring a slack cover without pulling it taut, overstating the required size.
- Confusing cushion thickness with chair-back clearance. A thick back cushion eats into usable seat depth, so check thickness and remaining space after installation.
- Assuming every maker uses the same convention. Some say add 1 inch to width and depth; others say compare your numbers directly against broadest-point specs. Read the maker’s instruction first.
Cushion.com notes that outside-frame width is the most frequent cause of an oversized order — a cushion that fits the chair but leaves no room between the arms.
If you’re buying a separately sold indoor seat cushion, federal rules may apply. Under 16 C.F.R. Part 1640, covered upholstered furniture made, imported, or reupholstered on or after June 25, 2021 must meet TB 117-2013 smolder-resistance requirements, and products made on or after June 25, 2022 carry a permanent label reading “Complies with U.S. CPSC requirements for upholstered furniture flammability.” A legitimate cushion will show that label.
Common Questions
Should I add an inch to my measurements?
Only if the maker says so. Cushion.com recommends adding 1 inch to width and depth for one-piece and bench cushions, but Polywood’s guide says to compare recorded measurements directly against broadest-point specs. Follow the product page — adding an inch unprompted produces an oversized cushion.
Do I measure the chair or the old cushion?
Both, in that order. Measure the chair’s usable seat area first, since that’s the space the cushion must fit. Then measure the old cushion for thickness and as a cross-check on width and depth. If the old cushion fit poorly, the chair measurement counts.
What if my chair seat is curved or tapered?
Take each side at its broadest point rather than a single measurement along the front edge. Polywood’s guidance notes that rounded and tapered designs need dimensions at the widest points, because a top-edge reading can understate the needed size.
Sources
- Cushion.com. “How to Measure Your Chair for a Cushion” Source for width, depth, thickness, back cushion, one-piece, and bench measuring steps and the 1-inch allowance.
- Polywood. “Cushion Sizing” Source for depth definition, deep-seating and irregular-shape guidance, and fabric-taut measuring.