Can I use a same-size insert?

You can, but the cover will look limp and the corners will stay empty. Sizing up one to two inches is what creates the full look.

Are down inserts worth the extra cost?

For bedrooms and formal rooms, yes — the drape is noticeably better. For everyday sofas with heavy use, polyester holds up with less effort.

Why do my throw pillows look flat?

Almost always an undersized insert, or a low-fill-weight polyester insert that has taken a permanent set. Check the fill weight before you buy.

Can I wash throw pillow inserts?

Polyester inserts usually yes, on gentle and dried fully. Down and feather inserts can be washed too, but they must be dried completely with dryer balls or they clump.

How many throw pillows should a sofa have?

Odd numbers look best on a standard three-seater — usually three or five, arranged large to small from the outside in.

What Size Throw Pillow Insert Do I Need?

4 min readUpdated 2026

Nearly every sad, wrinkled throw pillow has the same cause: someone bought an 18-inch insert for an 18-inch cover. Decorative covers are meant to be stuffed, so the insert needs to be larger than the cover to fill the corners and give the plump, upholstered look you were after. The rule is simple, and once you know it the rest is fill choice.

The rule: size up by 1 to 2 inches

Buy an insert one to two inches larger than the cover in each dimension. One inch up gives a neat, tailored look; two inches up gives a full, high-end look with sharp corners. Anything matched exactly will sag, and anything three inches up will strain the seams and the zip.

16 in cover → 18 in insert
18 in cover → 20 in insert
20 in cover → 22 in insert
22 in cover → 24 in insert
24 in cover → 26 in insert
12 × 20 in lumbar cover → 14 × 22 in insert

Which fill to choose

Fill decides how the cushion behaves once it is on the sofa, and the two common options behave very differently.

Feather-down inserts drape softly, karate-chop into that dented top shape, and look expensive — but they need daily fluffing and can poke through thin covers.
Polyester inserts hold a rounded shape with no maintenance, cost far less, and are washable — but they flatten over a couple of years and never get that soft slump.
Feather-down for beds and low-traffic sofas; polyester for family rooms, kids, and anyone who does not want to fluff.

Common sizes and where they go

Standard practice is largest at the back, working smaller toward the front.

24–26 in: floor cushions or the back layer on a large sectional.
20–22 in: main sofa cushions and the back row on a bed.
18 in: the workhorse size — the middle layer almost everywhere.
16 in and under: accent cushions on chairs and window seats.
12 × 20 in lumbar: front layer, and the one that is actually comfortable to lean on.

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