For a 16×16 throw pillow cover, a 17×17 insert gives the fullest standard look, though an 18×18 insert works if you want an extra-plump, overstuffed feel.
A cover that fits perfectly flat when empty will look flat when it’s zipped shut — the fabric pulls tight, the corners slump, and the whole thing reads as tired rather than styled. The fix is simple: the insert should almost always be bigger than the cover, not the same size. That gap is what fills out the corners and gives the pillow its shape.
This guide covers the sizing rule that actually works, when to break it, and how to measure a cover whose label you don’t trust.
Why The Insert Should Be Bigger Than The Cover
An insert one to two inches larger than the cover is the most consistent rule for square decorative pillows, and it’s the difference between a pillow that looks stuffed and one that looks deflated. A 16×16 cover with a 16×16 insert leaves the cover stretched to its absolute limit with nothing left to round out the corners. Sizing up gives the fill room to expand into the seams.
The heavy-fabric exception matters here. Thick covers — boucle, heavy linen, tapestry weaves — eat an extra half inch of insert volume compared to a thin cotton or velvet cover. If your cover is on the heavy side, lean toward the upper end of the range or step up a full size.
- 17×17 insert: the default sweet spot for a 16×16 cover; full and firm without looking overstuffed.
- 18×18 insert: use for a very plump, almost overstuffed look; best with square covers and heavy or loose-weave fabrics.
- 16×16 insert: works only if you want a flatter, more tailored pillow — expect soft corners.
- Feather inserts: compress more than polyester, so the same size reads slightly thinner; sizing up one inch still applies.
How Do You Know Which Insert Size To Buy?
Measure the cover yourself instead of trusting the tag, because loose manufacturing tolerances mean a “16×16” cover can actually measure 15.5 or 16.5 inches once you account for seam allowance. Lay the cover flat, then run a tape seam-to-seam across the full width and the full height. Whatever number you get, add one to two inches for the insert.
If the cover is already stuffed and you can’t measure it flat, wrap a soft tape loosely around the pillow’s widest girth, seam-to-seam, and divide that number in half to estimate the flat size. Then apply the same one-to-two-inch bump.
| Cover Measured | Best Insert Size | Look It Produces |
|---|---|---|
| 16×16, light fabric | 17×17 | Full, natural corners |
| 16×16, heavy fabric | 17×17 or 18×18 | Firm, filled edge-to-edge |
| 16×16, want max plump | 18×18 | Overstuffed, dense |
| 15.5×15.5 actual | 17×17 | Full with a little slack |
| 16.5×16.5 actual | 18×18 | Plump, no empty corners |
Brands like Utopia Bedding and Foamily both list 16×16 throw pillow inserts, but a listing page only tells you the insert exists in that size — it says nothing about how it pairs with your specific cover. Match the insert to your cover’s measured dimensions, not to the number printed on the product page.
Common Sizing Mistakes To Avoid
Buying an insert the same size as the cover is the single most common mistake, and it’s the one that produces a pillow nobody wants to display. The cover looks tight and flat, the corners stay empty, and no amount of fluffing fixes it.
Ignoring fabric weight is the close second. A heavy cover wrapped around a too-small insert won’t stretch to fill the gaps, so the pillow reads as lumpy rather than full. When in doubt on a thick cover, go one size larger than you otherwise would.
Assuming a decorative pillow will do double duty as back support is worth flagging too. A 16×16 throw pillow is a styling accent, and smaller decorative sizes generally aren’t sized to give an adult real lumbar support — treat it as decor, not a functional cushion.
If you’re still comparing options before you commit, this roundup of the best 16×16 throw pillows walks through covers and inserts side by side. For the filler itself, ComfyDown makes a feather-and-down decorative insert sold specifically in the sizing range this cover needs. Feather fill compresses more than polyester over time, so if you go that route, expect to size up rather than down. Whichever you pick, buy the insert to match your cover’s measured size, not your cover’s label.
FAQs
Will an 18×18 insert fit in a 16×16 cover?
It fits, but only because the cover fabric stretches to accommodate it. An 18-inch insert in a 16-inch cover produces a dense, overstuffed pillow with a firm, almost rigid shape. That look works if you want maximum plumpness, but it can stress the zipper and seams over time. A 17×17 insert is the safer default.
Should the insert be bigger or smaller than the cover?
Bigger, by one to two inches. A smaller insert leaves the cover loose and the corners empty, which is why a 16×16 cover paired with a 16×16 insert typically looks flat. Sizing up lets the fill push out into every corner and keeps the pillow looking full and intentional.
Does fabric thickness change the insert size I need?
Yes. Thick cover fabrics — boucle, heavy linen, tapestry — swallow more of the insert’s volume, so the pillow can look underfilled even with a correctly sized insert. For heavy covers, size up toward the larger end of the one-to-two-inch range, or step to a full 18×18 insert for a firm, full look.
References & Sources
- Utopia Bedding. “Utopia Bedding Throw Pillow Insert, 16×16 Inch.” An example of a 16×16 insert sold for this cover size.
- Foamily. “Foamily Premium Hypoallergenic Polyester Throw Pillow Insert, 16×16 Inch.” Another 16×16 insert option that exists in this size.
- ComfyDown. “ComfyDown Feather and Down Square Decorative Pillow Insert.” A feather-fill insert relevant to sizing notes.
