How big should I cut the cover for the pad?

This is a flat (knife-edge) cover, so the plumpness comes from the pad filling, not from a boxing strip — you never add the pad depth to the cut. Cut the front panel the same size as the pad plus your seam allowance on each edge (with a 1.5cm seam allowance that is pad + 3cm overall). For a very plump finish on polyester pads, many UK sewers cut the front exactly pad-size with no seam allowance so the cover sits 1-2cm under-size and fills out tightly.

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. Each panel is the width of the front, half the front height plus part of the overlap, with a double-fold hem on the opening edge. 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.

Do I need extra fabric for velvet or a patterned print?

Yes. This estimate assumes a plain, non-directional fabric. For velvet or any napped/one-way fabric, lay every piece in the same direction (the pile must run the same way), which uses more fabric. For a large print or check you want to centre or match, add at least one full pattern repeat to the length per major piece. Add a generous 5-10% over the figure shown to cover both.

SewCalcs

Cushion Cover Calculator — Fabric & Zip

Calculate fabric for cushion covers with zip or envelope back.

Cushion Pad Size

Square pad edge, e.g. 45cm

Back StyleEnvelope (no zip) or zip closure

Quantity

Number of covers to make

Fabric Width

Usable bolt width (UK: 137-150cm furnishing, 110cm cotton)

Fabric Price (optional)

Fabric cost per metre, for a total estimate

How We Calculate This

This is a flat (knife-edge) cover: the front panel is cut to the pad size plus a seam allowance on each edge, and the pad filling provides the plumpness. Envelope backs use two overlapping panels; zip backs use a single back panel plus a zip.

The formula

Front cut = Pad size + (Seam allowance × 2)

Envelope back: 2 panels, each = front width × (half front height + half overlap + double-fold hem)

Zip back: 1 panel the same size as the front

Add extra for velvet/napped fabric (lay all pieces one-way) and for matching a large pattern repeat.

Frequently Asked Questions

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Last updated: February 2026

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