---
title: "Trapezoid Cushion Calculator + Printable 1:1 Template"
url: "https://cushionguide.com/studio/trapezoid-cushion-calculator/"
---

*Enter any three of front, back, depth, side or angle to get the rest, check that your sketch closes, and print a full-size template on A4 or Letter paper.*

The Studio · Calculator

# Trapezoid cushion calculator

Every odd shape is just a list of honest measurements. Give me three of them and I will give you the rest, check your sketch to ± ¼ in and print the pattern at full size.

Worked out by [Nate](https://cushionguide.com/masters/nate/)

The Pattern Engineer of Detroit · January 27, 2026

## The quick answer

Three measurements decide a trapezoid cushion: front width, back width and the straight depth between them. For a symmetric shape each slanted side is √(((front − back) ÷ 2)² + depth²), and it is always longer than the depth. Enter any three values and the calculator returns the rest, checks your sketch and prints a 1:1 template on A4 or Letter sheets.

## The trapezoid cushion calculator

Every field is live. Change a number and the drawing redraws; copy the link and it opens with your numbers.

Load an example — the ones marked are past projects

Drawing…

Drawn to scale. Angles inside the shape; the dashed outline is the cut line when a seam allowance is added.

## Buyer questions

## The dog, the linen and the corners that weren't square

A buyer with a dog chose washable linen for a long angled window seat and sent a sketch: 112 in along the long edge, 18 in deep, end sections of 32½ and 31 in, and slanted edges written as 35 in. The first photo was blurred; the second was sharp enough to draw to scale — and the drawing disagreed with the 35 in. The corners were not square.

The workshop did what I would do, partner: kept the edges that sit against walls as the masters — 112 in, 18 in, 32½ in and 31 in, which make the short edge about 48½ in — and let the diagonals fall where the geometry puts them. Small differences disappear into the foam and the sewing tolerance. The buyer confirmed, and it went into production.

**The lesson:** when a sketch argues with itself, decide which measurements touch walls. Those are the truth.

## How to use it

Angles are just lengths in disguise. Three edges and a depth, and you never need a protractor.

Most dining chairs need one of these two outlines; a trapezoid is wider at the front than at the back.

## Questions people ask

### How do you calculate the slanted side of a trapezoid cushion?

Halve the difference between front and back, then use Pythagoras with the depth: side = √(((front − back) ÷ 2)² + depth²). For a 48 in front, 36 in back and 18 in depth: √(6² + 18²) = 18.97 in, about 19 in.

### Why must the slanted side be longer than the depth?

Because the depth is the shortest distance between the front and back lines. Any slanted edge between the same two lines is longer; if your sketch says otherwise, one of the numbers is wrong.

### How do I work out the corner angle of a trapezoid cushion?

The front-corner angle is the arctangent of depth ÷ set-back, where the set-back is (front − back) ÷ 2 for a symmetric shape. 18 in of depth and a 6 in set-back give 71.6°, which is 18.4° off square.

### Can I print a trapezoid template at full size at home?

Yes. The template is split into Letter or A4 sheets with overlap bands and sheet names. Print at 100 % with “fit to page” switched off, check the calibration square, then tape the sheets together.

### Is a trapezoid cushion made differently from a rectangle?

It takes extra cutting and sewing, so workshops usually price and produce it separately. More than one trapezoid has been ordered as a rectangle and had to be re-ordered with the drawing attached.

Nate Kowalski

The Pattern Engineer of Detroit, Michigan

A mechanical engineer who spent ten years designing car seats for a Detroit supplier, then quit to join his uncle's upholstery shop in Hamtramck.

± 1/4 in — Nate

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