What envelope fits my card?
Type the size of what you're mailing. We'll suggest envelopes with at least ⅛″ of total clearance in each direction (the tightest standard, used by A2) and tell you how USPS classifies it by size.
Popular answers
- 5×7 card → A7 (5¼×7¼). Details
- 4¼×5½ card → A2
- Letter paper folded in thirds → #10
- A4 folded in thirds → DL
- Square card → square envelope, but expect a surcharge
Sources
- USPS DMM 101 – Physical standards for letters, flats, parcels
- USPS DMM Notice 123 – Price list (nonmachinable surcharge)
- Envelope Sizes & Dimensions chart (The Letter Pilot)
- Paper Papers – envelope sizes guide
Checked 2026-10-21. Postal rules change; confirm with USPS before a large mailing.