How to Choose a 16×16 Pillow Insert | Fullness Guide

For a 16×16 pillow cover, choose a 17×17 insert for a fuller, corner-filling look or a 16×16 for a softer, slouchier fit.

Choosing the right insert for a 16×16 cover comes down to one decision: how full you want the pillow to look. A same-size insert leaves the cover loose and casual, while going up a size creates that crisp, plump look found in catalog styling. The standard advice from pillow manufacturers is to size up.

Medley Home’s pillow insert guide, and most other manufacturers, recommend an insert 1 to 2 inches larger than the cover for square pillows. That rule puts a 17×17 insert as the default pick for a 16×16 cover. Some prefer an 18×18 for an extra-plump look, though that size pushes the limit of what the cover can hold comfortably.

The Rule of Thumb for Insert Size

Square pillow covers almost always look better with an insert that’s slightly oversized. The general guidance is to buy an insert 1–2 inches larger than the cover, which means a 17×17 insert for your 16×16 cover.

The reason is simple: a cover that’s the exact same size as its insert has no room to stretch, so the corners stay flat and the pillow looks under-filled. An insert that’s a bit larger fills out the corners and gives the pillow that “styled” appearance instead of a floppy one.

While 17×17 is the sweet spot for most people, some prefer an 18×18 insert for an even fuller finish. The trade-off is that an 18×18 insert can strain the seams of a 16×16 cover, especially if the fabric has no stretch. Stick with 17×17 unless you specifically want a drum-tight pillow and your cover is made from a sturdy, non-delicate fabric.

16×16 Fit Variations: Same-Size vs. Oversized

The insert size you choose changes the look and feel of the finished pillow in predictable ways. Here’s what each option delivers on a 16×16 cover:

• 16×16 insert: Soft, slouchy, and casual. The pillow will look relaxed and under-stuffed, with corners that stay a bit flat. This works for a laid-back look where comfort trumps structure.
• 17×17 insert: Full and polished, with corners that fill out properly. This is the recommended size for most 16×16 covers and matches what Medley Home and other guides suggest for both down and polyfill inserts.
• 18×18 insert: Extra plump and drum-tight. This creates the fullest possible look, but risks straining seams or making the cover feel stiff. Use it only with durable fabrics and check that the zipper or opening can handle the stress.

Keep in mind that a 16×16 insert will make the pillow feel softer and floppier, while a larger one creates a more structured, corner-filled appearance. If you’re not sure which you want, consider that most people find the 17×17 to be the “just right” balance — full enough to look intentional, but not so tight that the seams are stressed.

How to Measure Your Cover First

Before buying an insert, measure the cover properly so you know exactly what size you’re working with. One common mistake is measuring with a ruler across the exterior of a cover that’s been sewn with a seam allowance, which gives you a slightly larger number than the actual interior space.

Instead, measure the cover seam-to-seam from the inside. Open the cover fully and measure from the inside edge of one seam to the inside edge of the opposite seam. This interior measurement tells you the true space the insert needs to fill. For most 16×16 covers, that interior measure will be slightly under 16 inches, which is exactly why a 16×16 insert looks loose and a 17×17 looks right.

If you’re styling a group of pillows, note that smaller decorative pillows like 16×16 are typically used for accent styling rather than functional back support. They’re meant to lean against larger sofas or beds as visual accents, not to prop up a person’s back for long periods.

When you’re ready to buy, our roundup of the best 16×16 pillow inserts on the market covers tested options by fill type and price.

Polyfill vs. Down: Does It Change the Size?

No — the recommended insert size stays the same regardless of fill material. Medley Home’s size chart lists 17×17 for both down/feather and polyfill when the cover is 16×16. What changes between fill types is the feel, not the size.

Down and feather inserts are softer and more malleable; they compress easily and drape nicely, which means they sometimes look a bit less full unless you go up a size. Polyfill inserts are firmer and hold their shape better, so a 17×17 polyfill will look noticeably plumper than a 17×17 down insert of similar quality.

If you’re going with down and want a really full look, the 18×18 option is slightly more forgiving than it is with polyfill, since down compresses more readily and puts less stress on seams.