---
title: "How to Measure a Trapezoid Cushion: Every Edge, One Depth"
url: "https://cushionguide.com/answers/trapezoid-cushion-measurements-needed/"
section: "The Cutting Table"
author: "Nate Kowalski, The Pattern Engineer of Detroit"
author_url: "https://cushionguide.com/masters/nate/"
published: "2026-05-12"
updated: "2026-05-12"
keywords: "how to measure trapezoid cushion, trapezoid bay window cushion measurements, clipped corner bay cushion, bay window seat measuring, custom trapezoid cushion"
---

# What measurements do you need for a trapezoid bay window cushion?

*Four sides, a depth and a thickness. Leave one out and the quote waits for it.*

Also asked as: How do I measure a bay window seat?; What measurements would you need?

> **The quick answer:** Send every edge of the trapezoid: the front, the back, both angled sides and any clipped corners, plus one straight depth and the thickness. Measure each angled side on its own, corner to corner, and take the depth straight down from the highest point to the base line. Add a drawing labeled A, B, C, D, a photo of the seat and any cut-outs.

![Dusty rose textured bay window seat cushion on a cream paneled base with a brass floor lamp, botanical prints and cosmos](https://cushionguide.com/media/bay-window-cushions/dusty-rose-bay-window-seat-sunbeams-botanical-1600.webp "Dusty rose crinkle-textured cushions follow the angles of a cream bay, lit by morning sun.")

## Key facts

- Every edge is measured: front, back, both angled sides and any clipped-corner or short end sides.
- Depth runs straight from the highest point down to the base line, never along a slanted side.
- Each angled side is measured separately, corner to corner.
- On a bay, every breaking point is measured, and cut-outs such as a window handle go on the drawing.
- A photo of the space and a drawing labeled A, B, C, D are requested; centimeters are preferred.
- A missing side is asked for before the quote.
- Very long trapezoids, such as 89 in (226 cm) on the long side, may be suggested in two pieces.

## Every number, in the order the cutter reads them

1. **A: the front edge**: Tape along the room side of the seat, end to end.
2. **B: the back edge**: The window side, corner to corner.
3. **C and D: each angled side**: Two separate readings. Never copy one onto the other.
4. **E, F: clipped corners and short ends**: Every small edge of a [clipped corner](https://cushionguide.com/glossary/#clipped-corner) gets its own letter and length. On a bay, so does every breaking point.
5. **The depth**: Straight from the highest point down to the base line, square to the front edge.
6. **The thickness**: The foam height you want. Mark any cut-out, such as a window handle, where it sits.

## Why the angled side is never the depth

Here is the mix-up I see most. On an angled bay, the slanted side always runs longer than the straight depth, so a drawing that repeats one number for both will not close. One sketch gave two sides of 43 in (109 cm) each; on that trapezoid they could not both be 43 in, so each side had to be measured on its own.

Another buyer in the US sent 86 in (218 cm) along the top, 126 in (320 cm) along the bottom and 26.5 in (67 cm) on each side. The cutting table worked the depth out from those sides: about 17.4 in (44 cm). Angles are just lengths in disguise. When numbers don't close, the depth is calculated and sent back for you to confirm.

Run your numbers through the [trapezoid cushion calculator](https://cushionguide.com/studio/trapezoid-cushion-calculator/) before you send them. The full method sits in the [trapezoid measuring Pattern](https://cushionguide.com/guides/trapezoid-cushion-measurements/), and finished seats live under [bay window cushions](https://cushionguide.com/cushions/bay-window-cushions/). What does your front edge read, partner?

## Long seats, units and the two-piece question

Very long trapezoids, around 79 in (200 cm) or more on the long side, may be suggested in two pieces. For one with an 89 in (226 cm) long side, the workshop asked whether two pieces would be acceptable before quoting it as one. Say in your note whether a split works for you.

Inches are fine. Centimeters are preferred at the cutting table, so if your tape shows both, write both.

> **Tailor's margin:** On an angled bay, the slanted side of a trapezoid cushion is always longer than its straight depth, so measure each side corner to corner.

> A trapezoid cushion with an 86 in top, a 126 in bottom and 26.5 in sides has a straight depth of about 17.4 in, not 26.5 in.
>
> — Nate

## Buyer questions

**A common question:** What do you need for a clipped-corner trapezoid bay cushion?

**The workshop's answer:** Every edge: front, back, both sides, any small clipped-corner edges, and the depth from the highest point straight down to the base line. If the numbers don't add up, the depth is worked out from the sides and you confirm it. Mark cut-outs such as a window handle too.

**A common question:** How should I send measurements for an odd-shaped bay window seat?

**The workshop's answer:** A photo of the space and a drawing with every side labeled A, B, C, D, plus the depth, ideally in centimeters. Measure every breaking point of the bay; a missing side such as D is requested before quoting.

**A common question:** Can you make a cushion for my trapezoid bay, and what do you need from me?

**The workshop's answer:** Yes. Send a drawing with every side measured, a photo of the space and the thickness; a size chart is provided. Measure the angled sides separately: on a trapezoid, two sides cannot both be 43 in.

**A common question:** Do you cut trapezoid cushions to measure, even long ones?

**The workshop's answer:** Yes. Send every side, including the long one. For a trapezoid with an 89 in (226 cm) long side, the workshop asked whether two pieces would be acceptable before quoting it as a single piece.

## Questions buyers ask next

### Can I send trapezoid measurements in inches rather than centimeters?

Yes. Buyers in the US send inches and the workshop works from them. Centimeters are preferred at the cutting table, so write both if your tape shows both, and keep every edge in one unit.

### Does a bay window cushion have to be symmetrical to be made?

No. Asymmetric bays are fine; the cushion is cut to your drawing. Order on the custom-shape listing, choose the size by depth and overall length, and upload a sketch with every edge and a photo of the seat.

### What if my bay has five windows and a lot of angles?

Any number of angles can be made. Sketch every segment with its length and the depth at each breaking point; the workshop turns it into a template for you to check, then you order by the nearest size range and write the full shape in personalization.

## Related at the atelier

- [Can you make a custom-shaped floor cushion for my corner or reading nook?](https://cushionguide.com/answers/custom-shaped-floor-cushion-corner-reading-nook/): A floor cushion can be made to the shape of your corner, bay or reading nook when you send the shape and measurements before ordering.
- [Can you make a cushion for a bay window with 5 windows, all at different angles?](https://cushionguide.com/answers/multi-angle-bay-window-cushion-5-windows/): Yes: a bay window seat cushion can have any number of angles, including 5-window, pentagon and hexagon bays.
- [How do I label the sides on my trapezoid cushion drawing?](https://cushionguide.com/answers/trapezoid-cushion-drawing-label-sides/): Give every edge of the trapezoid a letter and a length: A, B, C and D for the four sides, plus E and F for clipped corners or end pieces, then add the depth and thickness.
- [Bay Window Cushion With One Clipped Corner in a Bedroom](https://cushionguide.com/readings/hunter-green-clipped-bay-seat-cushion-bedroom/): A bay window cushion for a lopsided bay may need only one clipped corner: measure the back edge, the front edge and the depth at each end separately, then draw the shape.
- [Bay Window Cushion in Deep Teal with Clipped Corners](https://cushionguide.com/readings/deep-teal-clipped-bay-window-cushion-oak-frames/): A bay window cushion with clipped corners follows the short angled sides of the bay, and a box edge with piping on both the top and bottom seams makes it read as one neat slab.
- [Bay Window Cushion Corner Up Close: How Linen-Look Wears](https://cushionguide.com/readings/trapezoid-window-cushion-corner-detail-indigo-piping/): Oatmeal linen-look on a bay window cushion is a polyester weave that copies linen's matte, slubby surface but wrinkles and shrinks less than pure linen.
- [How to measure a trapezoid cushion so the numbers close](https://cushionguide.com/guides/trapezoid-cushion-measurements/)
- [Measuring a 3-sided bay window seat cushion, panel by panel](https://cushionguide.com/guides/bay-window-seat-cushion-3-sided/)

*± 1/4 in — Nate*

---

Written by Nate Kowalski (https://cushionguide.com/masters/nate/) for CushionGuide (https://cushionguide.com/about/). The site explains made-to-measure cushions and the partner workshop makes them; measurements are in inches first. This Markdown mirrors the page at https://cushionguide.com/answers/trapezoid-cushion-measurements-needed/