Should I add ease for the cushion pad?

Make the cover 1-2cm smaller than the pad for a plump look with standard polyester pads. For feather pads, make it the same size as the pad. The cushion depth (gusset) allowance accounts for the pad thickness.

What is an envelope back?

An envelope back has two overlapping panels instead of a zip. The overlap (usually 10-15cm) holds the cushion pad inside. It is the easiest closure method and allows easy pad removal for washing.

What size zip do I need?

Use a zip approximately 5cm shorter than the cushion width. For a 45cm cushion, use a 40cm zip. Concealed (invisible) zips give the neatest finish. Place the zip along the bottom edge.

What are standard UK cushion pad sizes?

Common UK sizes are 30cm, 35cm, 40cm, 45cm, 50cm, and 60cm square. Rectangular sizes include 30x50cm and 40x60cm. Always check your pad measurements before cutting fabric.

SewCalcs

Cushion Cover Calculator — Fabric & Zip

Calculate fabric for cushion covers with zip or envelope back.

Cushion Pad Size

Square dimension

Cushion Depth

Back Style

Quantity

Seam Allowance

Fabric Width

Fabric Price (optional)

How We Calculate This

The cover is cut slightly larger than the pad to accommodate depth. Envelope backs need two overlapping pieces; zip backs need one piece plus a zip.

The formula

Cut size = Cushion size + Depth + (Seam allowance × 2)

Envelope back: 2 pieces, each half + 35% overlap

Zip back: 1 piece same as front

Frequently Asked Questions

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Last updated: February 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.