---
title: "Bay Window Cushion Calculator: Every Piece, to Scale"
url: "https://cushionguide.com/studio/bay-window-calculator/"
---

*Enter your bay's wall sections and angles, or just its depth, and get a to-scale plan with every cushion piece: front, back and depth in inches and centimeters.*

The Studio · Calculator

# Bay window cushion calculator

Right, then. A bay seat is only awkward until every edge has a number on it. Give me the walls and the angles — or just how far the bay pokes out — and I'll draw the lot to scale.

Worked out by [Maggie](https://cushionguide.com/masters/maggie/)

The Piping Queen of Newport · February 17, 2026 · Updated March 24, 2026

## The quick answer

Measure each wall section along the back of the seat, plus either the corner angles, the bay's projection or the straight opening width. A three-sided bay with a straight front makes one trapezoid cushion; a seat that follows the bay makes one mitered trapezoid per wall. The calculator draws the plan to scale and lists every piece in inches and centimeters.

## The bay window 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…

Plan view, drawn to scale on graph paper. Hatched = walls, pale lines = glazing, dashed = piping line.

## Buyer questions

## The seat that measured 27 inches deep — on paper

A buyer sent a hand sketch of a big bay seat: 95 in along the front, 61 in at the back, 22 in on each angled side and 10½ in on the two short end edges. What the sketch didn't have was the depth. The workshop redrew it as a clean diagram and worked the depth out from the other edges: about 24½ in. The buyer's tape said 27 in.

Load *95 / 61 / 22 in* in the calculator above and you'll get the same 24½ in. When the edges and the depth disagree by 2½ in, dear, one of them is wrong. Here the real depth won, the drawing was revised, and production started only once the buyer had approved it.

**The lesson:** every angled cushion needs its front-to-back depth *as well as* the edges. Write both, and let the drawing argue with you before the scissors do.

## How to use it

Measure the bench, not the cushion you used to have. Old cushions shrink, sag and fib.

A rust bouclé cushion wraps every facet of a five-sided bay, with cream and sage pillows set on the central panels.

## Questions people ask

### What angle is a bay window?

Many three-sided bays are built at 45°, which reads 135° inside the seat, and some at 30° or 60°. Houses are rarely exact, so measure it: an angle finder on the seat board, or the projection and wall lengths, from which the calculator solves the angle.

### Should a bay window cushion be one piece or several?

A straight-fronted three-sided bay is usually one trapezoid. A seat that wraps around the bay can be one continuous piece (more work and fabric) or one cushion per wall section, which are easier to fit, turn and wash. Very long runs are often split into sections for handling.

### How do I find the bay angle without an angle finder?

Measure the side walls along the seat and either how far the bay projects from the opening line or the straight width across the opening. Choose that option in the calculator and it works out the corner angle.

### What if my bay window measurements don't add up?

Corners are rarely perfectly square. Treat the edges that touch walls as the master measurements and let the diagonals follow; a good workshop cuts from the main dimensions and absorbs small differences in the foam and sewing tolerance — after telling you.

### Can a curved bay window seat be calculated?

Not reliably from a few numbers. Faceted bays can; a smooth curve needs a full-size paper template traced on the seat itself.

Margaret Holloway

The Piping Queen of Newport, Rhode Island

Started out stitching costumes for a summer theater on the Rhode Island coast, then spent twenty years re-covering window seats in drafty Colonial and Victorian houses.

Stitch straight — Maggie

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