What Throw Pillow Insert Size Fits a 20x20 Cover?

A 20-inch cover takes a 22-inch insert — but the step-up varies by size

A 20x20 inch cover takes a 22x22 inch insert. That is the pairing to buy. Colin and Finn give exactly that worked example in their pillow insert size guide dated April 10, 2025, where the rule is a flat 2 inches larger, and the groundedinneutral chart posted April 29, 2025 lists the same pair, though it frames the size-up as a range of 1 to 2 inches. Two independent sources, one number. The problem starts when you carry the same two inches down to a 14-inch cover or up to a 30-inch euro.

Where the two rules split

Chloe & Olive's chart does not carry a fixed figure. It recommends an insert 1 to 4 inches larger depending on size, pairing a 14x14 inch cover with a 15x15 inch insert, a one-inch step-up, and a 30x30 inch cover with a 34x34 inch insert, which is four. Arianna Belle draws a similar line, recommending two inches all around for standard sizes, one inch for covers smaller than 18x18, and three inches once the cover reaches 24x24 inches or larger.

So the flat rule and the sliding rule sit alongside each other, and the sources do not reconcile them. Which one is right? Neither, at the sizes where they disagree; the evidence supports both and settles nothing between them. If you are choosing throw pillow insert size for a mixed arrangement, a pair of 20s, a 14-inch lumbar, a 26-inch euro against the back, one number cannot serve all of them. Chloe & Olive and Arianna Belle both say an insert that is too small looks saggy and flat. No source describes a failure mode for over-filling.

No source states a percentage rule or explains why a 30x30 cover would need four inches while a 14x14 needs one; the charts give paired sizes without a governing principle.

The Citizenry applies its +2 rule of thumb to euro shams as well.

Product	Size	Item Weight	Cover Material	Fabric Type	Right for
Utopia Bedding 18x18	18x18 Inch	16 ounces	Microfiber	Microfiber	Best multipack
FAVRIQ	20x20 Inch	16 ounces	Cotton	100% Cotton Cover	Best for 20-inch covers
Pillowflex Premium Polyester	20 Inch by 30 Inch	0.7 kg	Cotton, Polyester	Polyester Cotton Blend	Best oversized rectangle
ReynosoHomeDecor 10x13	10 Inches x 13 Inches	16 ounces	cotton-blend	Polyester Fibers,cotton	Best small lumbar
MIULEE	20x20 Inch (Pack of 1)	1.4 pounds	Polyester	Polyester Fibers	Best round shape

Every spec above is quoted from the listing; the “Right for” column is our judgement.

The short version

• The pick: Utopia Bedding 18x18, for refilling a whole sofa's worth of 16- or 18-inch covers at once, where buying inserts one at a time gets tedious.
• Also worth it: FAVRIQ, for the reader with 20-inch covers who wants the insert to actually fill them, and is willing to size up or down on purpose.
• How this was decided: published specifications and buyer reports across 5 products, compared below.

What do the charts leave out? Fill give and cover construction

Fill type matters, and no chart accounts for it. Chloe & Olive says down-feather inserts have more give than polyester or down alternative inserts, so fill can be worked into the cover's corners for a better fit.

The evidence file notes explicitly that the relationship between insert type and the size-up rule is untested by any source.

Arianna Belle's ranking of blends is the closest thing to a useful detail here: 95/5 feather/down is the firmest and most available, 90/10 sits softer than 95/5 and firmer than 80/20 or 75/25. Underfilled forms invert the rule entirely. Nadine Stay found Pottery Barn's down alternative needed at least a 4-inch size-up, and reported its 22-inch insert swimming inside a 20-inch cover.

No source in the evidence addresses whether a knife-edge, flange, piped or zippered cover changes the correct insert size.

Chris Loves Julia describes the Pillowflex form as dense, full and heavy with stiff corners. Foamily's polyfill, by the same test, has no fill in the corners and rebounds too fast to hold a chop.

Which one is yours

• Least number of items: Pillowflex Premium Polyester at 1.
• The middle of the range: MIULEE at 1.
• Most number of items: Utopia Bedding 18x18 at 4, worth it for refilling a whole sofa's worth of 16- or 18-inch covers at once,.

Before you order: what the sources do and do not settle

No source in the evidence says how insert or cover size is actually measured, whether the number is a flat-lay seam-to-seam figure, a finished measurement, or a fill-volume claim, and none says covers finish under label or that the +2" rule compensates for shrinkage:

• Fold the insert in half to load it, the method The Citizenry recommends, then release it into the corners.

Chloe & Olive and Arianna Belle both describe an insert that is too small as leaving the pillow looking saggy and flat. No source in the evidence describes what over-sizing does to a cover, or says which error is more common.

Inserts the sources tested

Nadine Stay tested six popular inserts, three down alternative and three feather down, and ranked Pillowflex first. Chris Loves Julia also placed Pillowflex first, at $30 for a 22x22". Every price point in the evidence is for a 22x22", so what these inserts cost in other sizes is not established.

Chris Loves Julia's own results describe the field:

• Edow, $13 for a 22x22" across six square sizes: arrived very flat with lumpy fill and is too lightweight to stand up.
• MoonRest, $26: arrives compressed and rolled and needs work to fluff, but comes in 40+ sizes, making it the pick when a very specific size is needed.
• Phantoscope, $24: stands on its own and holds a chop, though the reviewer wanted more density and weight.

Nadine Stay's feather results are mixed. Even her best-ranked feather insert, ComfyDown 95/5, sounded crunchy and had outer fabric thin enough that quills could poke through over time, and The Company Store's 95/5 was underfilled, flat and surprisingly lightweight. Its down alternative, by contrast, held its shape with minimal fluffing while being notably lightweight.

The Citizenry lists 20x26, 20x30 and 20x36 inches as standard, queen and king bed pillow sizes, and 18x18, 20x20 and 22x22 as common throw pillow sizes, with 26x26 and 28x28 common for euro shams. A commenter on Chris Loves Julia said none of the five tested inserts came in a size large enough for her couch pillows. No source addresses what to do when the sized-up insert does not exist.

Wrong-size inserts you already own

An insert that is one size too small is not wasted. Because most covers unzip, as Chris Loves Julia points out, the insert is the part you change, not the cover. No source in the evidence addresses adding fill, doubling up two inserts, or using an oversized insert in a stretch cover.

Density sometimes settles it. Arianna Belle notes that small rectangular forms such as a 10x18 are occasionally dense enough to fill a same-size cover, though no tested product in the evidence is matched to that case.

Which insert suits which case?

On the evidence available:

• Density and stiff corners: Pillowflex, which placed first in both tests.
• A very specific size: MoonRest, with its 40+ options.
• Lowest price: Edow at $13 for a 22x22".
• Not recommended: Foamily, which Chris Loves Julia declined to recommend and whose verdict there contradicts its Amazon reviews.

This comparison relies on two published hands-on tests, Chris Loves Julia's and Nadine Stay's; no source gives a fill-weight figure, and the reviews describe density only subjectively.

So the 22 holds at 20 inches for Colin and Finn and groundedinneutral. Carry it to a 30-inch euro and Chloe & Olive want 34. The sources do not settle the ground in between.

Which one, then?

Utopia Bedding 18x18, best for refilling a whole sofa's worth of 16- or 18-inch covers at once, where buying inserts one at a time gets tedious.

A different situation changes the pick:

• For the reader with 20-inch covers who wants the insert to actually fill them, and is willing to size up or down on purpose: FAVRIQ.
• For filling a 20x26 to 20x30 sham or long rectangular cover that square inserts leave visibly empty at the ends: Pillowflex Premium Polyester.
• For a small lumbar cover on an accent chair or window seat, where standard squares are far too big: ReynosoHomeDecor 10x13.

Before you order the Utopia Bedding 18x18: plush firmness means less push-back against a slouchy cover than a medium-fill insert