Window Seat Cushions

Window seat cushions come in two shapes, and only one of them goes wrong. The flat-window rectangle is easy. The bay is where every bad order I read about started, because it needs a trapezoid or a three-piece set and the angled returns are rarely 45 degrees even when they look it.

Measure the angles before you measure the lengths.

Thickness

Two to four inches, per This Old House, which repeats the range in its build guide. Today’s Homeowner suggests 3 inches minimum on top of the base.

Which end of that range you want depends on what the seat is for. A perch, where you sit facing out with your feet on the floor, works at the thin end. A lounge, where you sit sideways with your legs up for an hour, wants the thick end, because your hip bears the weight in one spot instead of spread across your thighs.

A window seat also usually sits on a hard box rather than a sprung base, so there is nothing under the cushion to give. That argues for the thicker end regardless.

Finished seat height should land around 18 inches from the floor, same as a dining chair. If your box is already at 17, a 4 inch cushion overshoots. More on the height arithmetic.

Measuring a bay window

This is the part that separates a cushion that fits from one that does not.

Measure the angles first. A bay window looks like it has 45 degree returns. Do not assume it does. Bay windows are built to several different angles and, as with any corner in a house, the built result drifts from the drawing. Interior walls can be half an inch out of line across 32 inches and still meet the NAHB performance guidelines.

Hold a piece of paper into each corner, mark where the walls cross it, and take that to the supplier. Or measure the diagonal across the corner and let them work the angle back.

Decide on one piece or three. A single trapezoidal cushion looks better and forgives nothing. Three pieces, one per section, cope with a wall that is not straight and are far easier to lift if there is storage underneath. Three is the safer order.

Take the depth at both ends of each section. Bay window boxes are often built to a drawing rather than to the room, so the depth at the left end of a section may not match the right. Order to the smaller.

Account for the window trim. The cushion sits on the box, but the back edge meets the window casing, which projects into the space. Measure from the face of the trim, not from the glass.

Subtract a quarter inch on each free edge. A cushion cut exactly to the box binds when you try to seat it, and it looks wrong because it bows up in the middle.

Check the sill height. If the sill is low enough that the cushion sits above it, you lose the backrest and gain a draught. Bob Vila’s rule for banquettes under windows is that windows want to be at least 24 inches off the floor to allow a 15 inch seat, not counting cushions. The same logic applies here.

Fabric and light

Window seats sit in direct sun, which is the one thing that separates them from every other cushion in the house.

Look for fade-resistant or solution-dyed fabric. Outdoor upholstery fabric is built for UV and is a reasonable indoor choice for a south-facing bay, even though it feels less soft. A standard cotton in full sun will show a line where the curtain fell within a couple of years.

Removable covers matter more here too, since the seat collects dust off the sill.

The ready-made market barely exists, and here is the evidence

I checked five window seat cushions on August 3, 2026. Two are out of stock or partially out of stock. Two more have 48 and 24 reviews, below the fifty this site requires. One passes.

On the two out-of-stock entries, the reviews are worth recording anyway, because they strengthen this page’s argument. Both are made-to-order cushions where the buyer specifies the size, and the low-star complaints on both are about size and cut accuracy, with no foam-flattening, shrinkage or fading complaints at all: “ordered 22" wide and considerably wider”, “does not appear to be rectangular”, “the cover is longer than the insert by atleast 2-3 inches”.

That leaves one ready-made recommendation and a clear argument for custom, which happens to be the truthful answer for window seats anyway. Bays have angles, sills are rarely square, and the window seat guide already tells readers to order three pieces rather than one and to measure the angles before the lengths. A stock rectangle cannot do that. A note on the “75D” in the table: that is the kg/m³ convention, and 75 kg/m³ works out near 4.7 lb/ft³, denser than the best custom foam grade sold. I read it as marketing. The foam density table on the bench cushions page shows what real grades measure.

1. ROFIEJOX Tufted Window Seat Cushion — the only stock option that holds up

Four inches, chenille, machine washable cover, 234 reviews at 4.6.

The fill is listed as high-density foam, memory foam and silk floss together, which is more detail than most listings give even if none of it is a number. Seven stock sizes run from 36 x 14 up to 72 x 14, plus a custom option, and that range is the widest here by some distance.

Specs. 36 x 14 x 4 in as tested. Fill listed as high-density foam, memory foam and silk floss. Density and ILD not published. Two end zips per reviewers.

Sold at: Amazon

2. Go custom, and what to specify

For a bay, a bench with a radiator cover, or any sill that is not a clean rectangle, made to measure is the answer, and the reviews above are the argument for it. Across the nine cushions I checked for this page and the bench cushions guide, five carried complaints about the delivered size not matching the listing. On a bench you can live with half an inch. In a window reveal you cannot.

One caveat first, because I checked: two of the cushions on this page are made-to-order in the buyer’s own dimensions, and their reviews still report wrong sizes. Ordering custom removes the guesswork about which stock size to pick. It does not remove the risk of a bad cut, so measure the delivered cushion on arrival and keep the return window in mind.

When you order, specify these four things, because a custom vendor will ask and a stock listing will never tell you:

Give them a density figure. The floor is 1.8 lb/ft³, and take 2.8 where the vendor offers it. Foam By Mail rates its 1.8 lb/ft³ HD36 at seven years against sixteen for the 2.8 lb/ft³ grade, at identical firmness.

Three inches minimum. FoamOrder says so, Today’s Homeowner says three inches minimum on a hard box, and This Old House puts the working range at two to four.

Solution-dyed fabric if the seat gets sun. Sunbrella is the reference, 100% solution-dyed acrylic with pigment added before spinning, carrying a five year limited warranty on upholstery weights. FoamOrder offers it. A surface-dyed cotton in a south-facing bay will not last a summer, and one of the cushions on the bench page has a reviewer describing it as shredded by the sun.

A removable cover with a zip. Four of the nine cushions I checked cannot be washed at all.

Custom vendors: FoamOrder · Cushion Source

Where to go next

I ran Corner Nook as a contract-grade furniture store from 2020. It now covers furniture for small spaces, corners, nooks, and rooms that have to do two jobs. More about who runs it. Every product here was checked for stock, seller and review history at the time of writing.