What Size Pillow Insert for a 20×20 Pillow Cover? | The 22-Inch Rule

For a standard 20×20 pillow cover, choose a 22×22 insert — an inch or two of extra fill keeps the corners sharp and stops the cover from sagging flat.

For the full breakdown, see our best 20 x 20 Pillow Covers guide.

A 20×20 cover paired with a 20×20 insert looks flat the moment anyone leans back on it. The cover measures 20 inches across, the insert measures 20 inches across, and the insert has to fill every corner of a slightly larger shell. It never quite does, and the corners stay empty while the center sags. Matching measurements feels logical, which is exactly why so many people buy the wrong size and end up with a limp, deflated-looking pillow.

The fix is counterintuitive but reliable: go bigger than the cover by 1–2 inches. Here’s how the sizing works, when to break the rule, and how to measure a cover whose label you don’t trust.

Why A Larger Insert Fills The Corners Better

An insert needs to be slightly compressed to look full.

That compression is what creates the plump, tailored look people expect from a decorative pillow. A same-size insert sits loose inside the shell, so the fill settles in the center, the edges go slack, and the pillow reads as underfilled even though it technically fits. Pillowfrenzy’s insert sizing guidance describes this directly: an insert 1–2 inches larger than the cover fills the corners and reduces sagging, and a 20×20 cover paired with a 20×20 insert is commonly described as flat-looking.

The general rule holds across makers. Mississippi Stitches’ sizing guidelines recommend sizing up so the insert fills out the cover, and Ariannabelle’s insert size guide gives the same default — 20×20 cover, 22×22 insert. A few practical notes sharpen it:

• Same size (20×20 insert): loose, flat corners, visible slack along the seams.
• One inch up (21×21 insert): adequate but slightly soft; a reasonable pick for stretchy or loosely woven covers.
• Two inches up (22×22 insert): the widely cited default for a full, crisp, corner-to-corner look.
• Three inches up (23×23 insert): usually too much — the cover strains and the zipper or opening can gap.

Thicker, stiffer fabrics — heavy linen, canvas, tightly woven cotton — often need the full 2-inch jump or even slightly more, because the fabric itself eats interior space and resists stretching over the fill.

When To Size Down Instead

Not every 20×20 cover wants a 22×22 insert. A very soft, stretchy, or loosely knitted cover will look overstuffed if you follow the default blindly.

If the fabric gives easily, size closer to the cover — a 21×21 insert, or in rare cases a 20×20. Alternatively, keep the 22×22 insert and accept a firm, densely packed pillow rather than a soft one. The trade is simple: more fill means a crisper shape, less fill means a squishier pillow. Decide which look you want before you buy, because the cover alone doesn’t determine it.

If you’re still choosing the cover itself, browsing tested 20 x 20 pillow covers gives you a sense of how different fabrics behave before you commit to an insert size.

How To Measure A Cover Seam To Seam

Finished sizes vary by maker, and the label isn’t always the measurement you’ll get. Laying the cover flat and measuring it yourself is the only reliable check.

Lay the empty cover flat on a table and smooth out any wrinkles. Measure from one sewn seam to the opposite sewn seam — side to side and top to bottom — and write both numbers down. If your cover measures closer to 19 inches, a 21×21 insert usually fits better than a 22×22. If it measures a true 20 inches or a hair over, stick with the 22×22 default.

One caveat applies to every row: zipper openings and envelope closures limit how much insert you can stuff through them.

Down and down-alternative inserts compress more than polyester fiberfill, so a down insert can sometimes run a full size smaller and still look full once it settles.