What Size Pillow Insert for a 20 x 20 Cover: The Complete Sizing Guide?

For a 20 x 20 pillow cover, choose a 22 x 22 inch insert — two inches larger fills the corners, prevents sagging, and gives a full, tailored finish.

A 20 x 20 cover stuffed with a 20 x 20 insert is the most common throw pillow mistake: the case arrives, the insert goes in, and the whole thing looks deflated. The fix is simple — size up. Choosing the right pillow insert size for a 20 x 20 cover means reaching for a 22 x 22 insert, not a matching one, because the extra two inches of fill is what makes a decorative pillow look plump instead of sad. Below is the exact rule, the one mistake to avoid, and when the standard sizing breaks down.

Why Does A 20 x 20 Cover Need A 22 x 22 Insert?

A 22 x 22 insert is the correct pairing for a 20 x 20 cover because the extra two inches of fill is what actually fills the corners and keeps the pillow from looking flat. Insert-to-cover sizing follows a simple rule: pick an insert 1–2 inches larger than the cover. For square covers 18 inches and up, 2 inches is the number most guides land on, which is why 20 x 20 covers consistently point to 22 x 22 inserts.

The logic is physical. A cover sized at 20 x 20 has interior space that a same-size insert can’t fully press into — the corners stay loose and the center dips. An oversized insert compresses slightly when you zip the cover, and that compression is exactly what creates a full silhouette. The payoff is a pillow that holds its shape, resists sagging over time, and accepts a crisp “karate chop” in the middle if that’s the look you want.

How To Measure Your Cover Before Buying

Measure the pillow cover itself — seam to seam — before you buy the insert. Finished cover sizes can vary by maker, so the nominal “20 x 20” on the label is a starting point, not a guarantee.

1. Lay the empty cover flat on a table and smooth out wrinkles.
2. Measure from one sewn seam to the opposite seam across the width.
3. Repeat for the height, then compare both numbers to the label size.
4. Add 2 inches to each measurement to get your insert size.

If the cover measures a true 20 x 20, you’re after a 22 x 22 insert. If it runs slightly small, a 22 x 22 still works — the fill simply compresses a touch more.

Once you know your size, the next step is picking the fill — and it helps to compare tested options side by side. This roundup of highly rated 20 x 20 pillow inserts covers the models that hold shape best in real use.

When The Standard Rule Changes

Two situations break the standard 2-inch rule, and both are worth knowing before you order. Mississippi Stitches sizing guidance and Chloe & Olive’s insert guide agree on the basic math but flag the exceptions.

• Heavy or thick fabric. A densely woven or lined cover eats interior space. Most standard-fill inserts aren’t enough to fill it properly — check the specific fabric notes before you buy.
• Lumbar shapes. Lumbar pillows are sized and filled differently from squares, so don’t apply the 2-inch rule to them.
• Specialty shams. Tailored shams and other specialty shapes follow their own sizing, not the standard throw pillow guidance.

For standard square decorative covers, though, the 22 x 22 pairing holds. Arianna Belle’s insert-size guide and the other sizing references above all point to the same answer for a 20 x 20 cover.