How Many Stamps Per Envelope? A Weight-Based Guide
One of the most frequent questions about postage is: how many stamps do I need? The answer depends on weight, size, destination, and sometimes shape—but with a few simple rules, you can figure it out without a trip to the post office.
Quick rule: A standard rectangular envelope weighing up to 1 ounce needs one Forever stamp ($0.82). Each additional ounce adds $0.29. Use the weight table below for exact combinations.
Standard Letter Postage by Weight
| Weight | Postage Needed | Stamps | Example |
|---|---|---|---|
| Up to 1 oz | $0.82 | 1 Forever | Standard greeting card, one-page letter |
| 1-2 oz | $1.11 | 1 Forever + 1 Add'l Oz | Wedding invitation with RSVP card |
| 2-3 oz | $1.40 | 1 Forever + 2 Add'l Oz | Multi-page letter with photos |
| 3-3.5 oz | $1.69 | 1 Forever + 3 Add'l Oz | Thick document packet (letter max) |
Special Envelope Situations
| Envelope Type | Postage | Reason |
|---|---|---|
| Square envelope | $1.17+ (nonmachinable surcharge) | Square envelopes cannot go through sorting machines. Add $0.35 surcharge. |
| Rigid envelope | $1.17+ (nonmachinable surcharge) | Envelopes that do not bend require manual sorting |
| Envelope with clasp/string | $1.17+ (nonmachinable surcharge) | Clasps and strings catch in sorting equipment |
| Address parallel to short side | $1.17+ (nonmachinable surcharge) | Landscape-oriented envelopes are nonmachinable |
| Standard postcard (up to 4.25x6") | $0.65 | Postcard rate |
| Oversized postcard (up to 6x9") | $0.82 | Letter rate applies |
International Mail
| Mailpiece | Postage | Stamps |
|---|---|---|
| 1 oz international letter | $1.75 | 1 Global Forever stamp |
| International postcard | $1.75 | 1 Global Forever stamp |
| 2 oz international letter | $2.32 | 1 Global Forever + postage for additional ounces |
How to Weigh Your Envelope at Home
A basic kitchen scale works well for letters. Weigh the fully assembled envelope—with everything inside—before sealing it. If your scale only measures in grams: 1 ounce = 28.35 grams.
No scale? A standard sheet of paper weighs approximately 0.16 ounces. Four sheets plus an envelope is approximately 0.8 ounces—under the one-ounce limit. Add a few more sheets or a heavier cardstock insert, and you may cross the threshold.
Stock Up on the Right Stamps
Forever stamps, Additional Ounce stamps, and Global stamps—all at discount prices.
Browse All StampsFrequently Asked Questions
Can I use two Forever stamps for a 2 oz envelope?
Yes, but it is more expensive than necessary. Two Forever stamps = $1.64, while the actual postage required is $1.11. You are overpaying $0.53. Use one Forever + one Additional Ounce instead.
What if I put too few stamps?
The letter will be returned to you marked "Postage Due" or delivered to the recipient with postage due. Either way, it is delayed and inconvenient.
Do I need extra postage for a wax seal?
Wax seals can make an envelope nonmachinable, requiring the $0.35 surcharge. They can also add weight. Weigh the sealed envelope to confirm.
Sources and Scope
- U.S. Postal Service — Postal Explorer — Domestic Mail Manual, sections 101 and 201, physical standards for retail letters and cards.
- U.S. Postal Service — Postal Explorer — Notice 123 Price List, First-Class Mail retail prices, effective July 12, 2026.
Rates apply only when the mailpiece qualifies for the stated category. Weight estimates are planning aids, not a substitute for weighing and measuring the finished piece.
Postage rates are current as of July 12, 2026.