Scale to GramsHow Heavy Can a Letter Be With One Stamp?
Quick Answer
A First-Class letter with one Forever stamp ($0.78) can weigh up to 1 oz (28g). That is roughly 5-7 sheets of standard 20-lb printer paper inside a #10 envelope. Anything heavier needs additional-ounce postage at $0.29 per extra ounce.
Weigh Your Letter From a PhotoMax with 1 stamp
1 oz
28 grams
Sheets of paper
5-7
20-lb printer paper
Additional oz
+$0.29
per extra oz
The 1-Ounce Rule
One Forever stamp ($0.78) covers any First-Class letter up to and including 1 oz (28g). This includes the envelope itself plus everything inside it. The instant you tip over 1 oz, you need additional postage at $0.29 per extra ounce. There is no grace zone.
What Fits in 1 Ounce
A standard #10 envelope (the long business kind) weighs about 6.7g (0.24 oz) by itself. That leaves about 21g for contents. Common contents and their weights:
| Item | Weight | How many fit in 1 oz? |
|---|---|---|
| #10 envelope (empty) | 0.24 oz / 6.7g | — (always counts) |
| Sheet of 20-lb printer paper | 0.16 oz / 4.5g | 4-5 sheets |
| Sheet of 24-lb paper | 0.20 oz / 5.5g | 3-4 sheets |
| Folded greeting card | 0.5-0.7 oz / 14-20g | 1 card alone |
| Single 4x6 photo | 0.2 oz / 5g | 3-4 photos |
| Small check or coupon | 0.05 oz / 1.5g | many |
| Business card | 0.04 oz / 1g | many |
| Bubble pad | 0.4-0.6 oz / 10-17g | forces you to 2 oz |
Postage by Weight
If you go over 1 oz, here is what each weight range costs in 2026:
| Letter weight | Postage | Combination |
|---|---|---|
| Up to 1 oz ⭐ | $0.78 | 1 Forever stamp |
| Over 1 to 2 oz | $1.07 | 1 Forever + 1 additional-oz |
| Over 2 to 3 oz | $1.36 | 1 Forever + 2 additional-oz |
| Over 3 to 3.5 oz | $1.65 | Letter max weight |
| Over 3.5 oz | Use flat or package rate | No longer a letter |
Watch Out For These
Things that quietly push you over the 1 oz limit:
| Thing | Why it kills your stamp |
|---|---|
| Glossy or photo paper | 2-3x heavier than regular paper |
| A second sheet "just in case" | Often pushes you to 2 oz |
| Cards with thick paper | Many greeting cards are >1 oz alone |
| Foreign coins as a souvenir | Even a single coin can be 0.3 oz |
| Magnetic business cards | Surprisingly heavy |
| Glitter or embossing | Adds 0.1-0.3 oz |
| A small key or charm | Almost always over the limit |
What Happens If You Underpay
If you mail a letter with insufficient postage, USPS may return it to you marked "Postage Due" (you pay the difference plus a fee), deliver it to the recipient marked "Postage Due" (the recipient pays), or in rare cases destroy it. Almost always, the letter still arrives — just with a delay and a fee for someone. The cheap fix is to add a second Forever stamp when in doubt.
How to Quickly Estimate Without a Scale
A standard #10 envelope with up to 5 sheets of regular printer paper is almost always under 1 oz. A folded greeting card with a regular paper insert is usually 1.5-2 oz and needs 2 stamps. When in doubt, photograph the letter next to a credit card or coin for scale and use the AI Letter Weight Tool to estimate before mailing.
Frequently Asked Questions
How many pages can I mail with one stamp?+
4-5 sheets of standard 20-lb printer paper inside a #10 envelope. The envelope itself weighs about 0.24 oz, leaving about 0.76 oz for contents at the 1 oz limit.
How heavy is a standard letter envelope?+
A standard #10 business envelope weighs about 6.7g (0.24 oz) empty. A6 invitation envelopes are slightly lighter at 4-5g, and padded mailers are much heavier at 14g+.
How much does a sheet of paper weigh?+
A single sheet of standard 20-lb printer paper (8.5"x11") weighs about 0.16 oz (4.5g). Heavier 24-lb or 28-lb papers weigh 0.20-0.24 oz (5.5-6.5g) per sheet.
How much does a greeting card weigh?+
A standard folded greeting card weighs 0.5-0.7 oz alone, plus 0.4 oz for a typical card envelope. Most greeting cards push the total to about 1 oz exactly — risky with one stamp. Use 2 stamps to be safe.
What if my letter is 1.1 oz?+
You need to pay for 2 oz. USPS rounds up to the next ounce. A 1.1 oz letter costs $1.07 (one Forever + one additional-ounce stamp).
Can I send a letter without weighing it?+
For a thin letter (3-4 sheets), one stamp is almost always enough. For anything thicker, photograph it and use the AI Letter Weight Tool, or just add a second stamp. Better to overpay than have it returned.
How much does a #10 envelope weigh empty?+
A standard #10 (4.125"x9.5") business envelope weighs about 0.24 oz (6.7g) when empty. The window envelope variant is essentially the same weight.
Try These Tools
Put what you learned into practice with our free AI tools:
