What Size Pillow Insert for 16×16 Cover? | The Right Fill

A 17×17 inch insert is the best size for a 16×16 inch pillow cover, giving a full, tailored look.

Trying to figure out what size pillow insert for a 16×16 cover works best comes down to the look you want. The general rule is to buy an insert one to two inches larger than the cover so the pillow looks plump instead of flat and sad. For a 16-inch cover, that points straight to the 17×17 size.

Here’s the thing: a cover that’s the same size as the insert looks underfilled. The cover’s seams can’t stretch, so the down or poly fill can’t expand to fill the space, leaving you with a saggy, wrinkly mess. The extra inch or two gives the cover room to hold a cushioned, structured pillow that looks like it belongs in a catalog.

The Simple Insert Size Rule for Throw Pillows

When shopping for a pillow insert, the golden rule is to select one that measures 1 to 2 inches larger than the cover. This overstuffing principle exists because the insert’s fill needs some slack in the fabric to puff out. When you add that inch on each side, the cover stretches just enough to show off the shape without looking like a sausage casing.

For smaller covers like a 16×16, a one-inch increase is often enough. For larger covers, a two-inch jump is common. So for a 16×16 cover, that means grabbing an insert between 17×17 and 18×18.

17×17 vs. 18×18 vs. 16×16 Inserts: Which to Pick

The best choice depends on the finish you want. Number one selling point for a 17×17 insert is that it produces the classic, slightly full look that flatters most spaces. The pillow will have defined sides and softly rounded corners, sitting upright against a sofa or bed. An 18×18 insert will push that effect further, filling the cover to the corners and creating a firmer, almost marshmallow-plump shape. On the other hand, using a 16×16 insert will leave the cover looking flat, slouchy or underfilled—perfect if you’re aiming for a relaxed, slumped look.

Fit also varies with fabric thickness and fill type. A thick, woven cover with heavy fabric will eat up some interior space, so you might need that bigger 18×18 insert. A lightweight linen cover will show an 18×18’s corners more clearly and can look overstuffed. Down inserts tend to be softer and compress more, while polyester fiber fills hold their shape better and run firmer. A down insert in 18×18 might yield a softer feel than a poly fill in 17×17.

Measuring and Fitting Your Pillow Cover

Textile guides like the ones from Chloe & Olive and Eryn Home advise measuring your cover before ordering. For the most accurate number, turn the cover inside out and measure along the interior seams. This seam-to-seam measurement reflects the actual usable space, which can be slightly smaller than the outside dimensions because the seam allowance takes up some fabric. Once you know that number, you can confidently choose the next size up for a standard look.

After sliding in the insert, check the closure. A too-large insert can strain the zipper or overlap the envelope flap, which is why some prefer the 17 over the 18 if the cover is snug. If the pillow is too big, it won’t be able to lay flat. If it’s too small, it will gather and wrinkle. Both outcomes are easy to fix only by buying the other size, so it’s worth measuring the first time.

There’s one exception to the overstuffing rule: Some brands produce covers cut generously, so a same-size insert might fit fine. Unless a specific cover lists its own sizing note, treat the one-inch rule as your starting point.

If you want to skip the guesswork on fill quality and price, our tested roundup of the best 16×16 pillow inserts covers the top options on the market right now.

For decorative throw pillows, that extra inch makes all the difference. A 17×17 insert offers the safest, best-looking fit for nearly every 16×16 cover, while a 16×16 insert only works if you want a deliberately underfilled look. Aloria’s sizing guide and the other manufacturer charts back up the same math: go one inch up as your default, two inches up if you want it packed full and your cover’s fabric can handle it.