Pillow Insert Size Calculator
Choose the right pillow insert size for a cover so it looks plump, and get the fabric cut size for the cover.
How it works
Insert = finished cover + oversize (0/1/2 in) · Cover cut panel = finished + 2 × seam allowance
A pillow insert should be slightly larger than its cover so the filling pushes into the corners and the pillow looks full instead of limp and empty-cornered. One inch bigger reads as neat and tailored; two inches gives that plump, showroom look. The second result gives the cut size for each cover panel so your finished cover ends up at the size you entered.
Worked example
For an 18×18 in cover with a plump look, add 2 inches to get a 20×20 in insert. To sew that cover with half-inch seams, cut each fabric panel 18 + 2 × 0.5 = 19 in square.
Frequently asked questions
Why use an insert bigger than the cover?
A same-size or smaller insert leaves the corners flat and the cover wrinkled. Sizing the insert one to two inches larger forces the fill into the corners so the pillow looks full and holds its shape.
Down versus polyester — does the size rule change?
Down and feather inserts compress more, so lean toward the plump +2 in option to keep them from looking deflated. Firm polyester or foam inserts hold their shape, so +1 in is usually enough.
What seam allowance should I cut for the cover?
Half an inch is standard for home-dec pillows. The cover cut-size result already adds your seam allowance to both edges, so the finished cover matches the size you typed.
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This calculator is for educational purposes. Double-check important results before acting on them.