Envelope & Paper Size Matcher
Choose the paper and the fold, and we’ll name the envelope that fits and show the folded size — no more letters that won’t go in or cards that arrive crumpled.
Match the paper to the envelope
Half the frustration of a first letter is the envelope: too small and the paper crumples, too big and it flops around. Matching them is easy once you know the fold. Fold in thirds for a long business envelope, in half for a squarer card envelope, or keep it flat for artwork you want to arrive pristine. This matcher does the sizing so a child can focus on the writing.
Once the envelope is chosen, work out the postage with the Postage Calculator— flat and oversized envelopes often cost a little more than a folded letter.
Frequently Asked Questions
What envelope fits a normal sheet of paper?
A US Letter sheet folded in thirds — the standard 'letter fold' — slides into a No. 10 business envelope, the long one most homes have. Folded in half it needs a taller A9 envelope, and left flat it takes a 9-by-12 flat envelope. Choose your paper and fold above and the tool names the smallest envelope that fits.
How do I fold a letter in thirds neatly?
Lay the sheet portrait, bring the bottom edge up to about one-third from the top and crease, then fold the top down over it so the three panels stack. The trick is to make the bottom fold slightly under a third so the top panel covers it. Done right, the folded letter drops straight into a No. 10 envelope.
Why leave a little margin inside the envelope?
Paper needs room to slide in and out without tearing, so the tool leaves about a quarter-inch of slack on each side when it picks an envelope. If a folded letter is a snug fit, fold it once more or step up to the next envelope size rather than forcing it and creasing the corners.
Can we mail a sheet without folding it?
Yes — a flat envelope (such as 9-by-12) keeps artwork, certificates, or a child's careful handwriting from getting creased. Flat mail is usually charged as a large envelope rather than a letter, so check the cost with the Postage Calculator before choosing to send it flat.
Sizes use common US paper and envelope standards in inches, with about a quarter-inch of margin. Check an unusual envelope against your paper before mailing.