Envelope size calculator
Find the smallest standard envelope that fits your document or flat item.
How it works
An envelope needs to be a little bigger than its contents in both directions, and thicker contents need more room because the envelope wraps around them. The calculator adds the thickness plus a quarter inch to each dimension, then finds the smallest standard size that fits.
Letter-size paper (8½ × 11 in) fits a 9 × 12 envelope flat, or a #10 envelope folded in thirds. In the US, items thicker than ¼ in are mailed as large envelopes (flats) and items over ¾ in as parcels, which cost more. For thicker items, see the poly mailer size calculator.
Results are estimates based on typical industry values. Confirm final specifications with your supplier or carrier.
Frequently asked questions
What envelope fits 8.5 × 11 paper without folding?
A 9 × 12 inch envelope.
What is a #10 envelope?
The standard US business envelope, 4⅛ × 9½ inches, which holds a letter folded in thirds.
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