Cushion Insert Size Guide

Choose a cushion insert about 5cm (2 inches) bigger than your cushion cover. A 45 × 45cm (18") cover takes a 50 × 50cm (20") insert for a full, plump finish. Matching sizes exactly is the most common mistake — it leaves cushions saggy with empty corners.

What size cushion insert do I need for my cover?

Why should the insert be bigger than the cover?

Covers relax with use; an insert one size up keeps the fabric taut, fills out the corners, and holds its shape after plumping. A same-size insert gives an intentionally flat, tailored look — fine for a minimalist scheme, but most people prefer the fuller finish.

When should the insert match the cover size?

Choose a same-size insert for stretchy or crocheted covers (they already grip the pad), waterproof or outdoor covers that have no give, and very structured box cushions.

How do I measure a cushion cover?

1. Turn the cover inside out.
2. Measure seam to seam across the width.
3. Measure seam to seam from top to bottom.
4. Use the smaller figure if they differ — covers stretch slightly in use.

Why does my cushion look flat and empty at the corners?

The insert is too small, or the filling has compressed. Go one size up, or for hollowfibre inserts, plump daily and replace roughly every 1–2 years of daily use.

Why does my cushion cover strain at the seams?

The insert is more than one size too big. Drop down one size — the seams should sit flat with no puckering.

Frequently asked questions

What is the most common cushion insert size in the UK?

45 × 45cm (18 × 18") — it fits the most widely sold cover size and suits standard sofas.

Are cushion pads and cushion inserts the same thing?

Yes — the terms are interchangeable; both mean the filled inner that goes inside a decorative cover.

What filling is best for everyday sofa cushions?

Hollowfibre — it plumps back readily, is machine-washable at home, and suits allergy-prone households better than feather.

How many cushions fit on a standard sofa?

Two 45cm cushions per seat on a 2-seater; a 3-seater takes 3–5 mixed sizes for a layered look.

Can I wash a cushion insert?

Hollowfibre inserts usually machine-wash at 40°C — check the care label; wash covers separately.

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Written by the Posh Tag team, Rochdale, Lancashire. Published: 12 July 2026 · Last reviewed: 12 July 2026.