What is the weight limit for a Forever Stamp?

A Forever Stamp covers postage for letters up to 1 ounce (28.35 grams). Letters between 1-2 oz require an additional ounce stamp ($0.29). Over 2 oz, you need additional postage based on USPS weight tiers.

What happens if my letter weighs more than 1 oz?

If you mail a letter over 1 oz with only one Forever Stamp, USPS will return it to you marked "insufficient postage" or deliver it with postage due for the recipient to pay.

Can I use two Forever Stamps for a 2 oz letter?

Yes, but it costs more than necessary. Two Forever Stamps = $1.56, while the correct rate for 2 oz is $1.07 (one Forever + one additional ounce stamp at $0.29).

How many sheets of paper can a Forever Stamp cover?

Typically 1-5 sheets of standard 20 lb paper in a regular envelope stay under 1 oz. 6-10 sheets usually push into the 1-2 oz range requiring additional postage.

Do Forever Stamps have size limits too?

Yes. Forever Stamps apply to letters meeting USPS letter-size standards: maximum 11.5" long, 6.125" high, 0.25" thick. Larger or thicker mail is classified as a flat or package with different rates.

Will USPS accept a slightly overweight letter?

No. USPS processes mail using automated scales. Even letters just over 1 oz are flagged and returned or marked postage due. Always add extra postage if you're close to the weight limit.

How do I weigh my letter at home?

Use a digital kitchen or postal scale. Most postal scales are accurate to 0.1 oz. If your letter weighs 0.95-1.0 oz or more, add an additional ounce stamp to be safe.

Forever Stamp Weight Limit: How Much Can You Mail? (2026)

A Forever Stamp covers postage for letters up to 1 ounce. Go even slightly over that limit, and you'll need additional postage — or risk having your mail returned.

Forever Stamps currently cost $0.78 (rising to $0.82 on July 12, 2026), and they're designed for standard letter-size envelopes within specific weight and size constraints. Understanding these limits prevents delays, returned mail, and postage-due charges.

The 1-Ounce Rule: Weight Limit Basics

One Forever Stamp = up to 1 ounce. This is the firm cutoff. USPS automated sorting equipment weighs each piece of mail, and anything over 1.0 oz gets flagged.

Quick Reference

Up to 1 oz: 1 Forever Stamp ($0.78)
1-2 oz: 1 Forever Stamp + 1 additional ounce stamp ($1.07 total)
2-3 oz: 1 Forever Stamp + 2 additional ounce stamps ($1.36 total)
3-3.5 oz: 1 Forever Stamp + 3 additional ounce stamps ($1.65 total)

What Weighs 1 Ounce?

In practical terms, 1 ounce typically includes:

1-5 sheets of standard 20 lb printer paper in a regular #10 envelope
A single-page letter with one or two photos (4x6 size)
Most greeting cards in a regular envelope
A check, invoice, or single-page legal document

Once you add 6+ sheets, a thick card, or bulky inserts, you'll likely cross into the 1-2 oz range and need additional postage.

Size Limits: Forever Stamps Aren't Just About Weight

Forever Stamps apply to letter-size mail — not just letters under 1 oz. USPS defines letter-size as:

USPS Letter-Size Standards:

• Minimum: 5" long × 3.5" high × 0.007" thick
• Maximum: 11.5" long × 6.125" high × 0.25" thick
• Must be rectangular and flexible

If your envelope exceeds these dimensions — like a 9×12 envelope or a rigid cardboard mailer — it's classified as a flat or package with different (higher) rates, regardless of weight.

What Happens If You Go Over 1 Ounce?

USPS doesn't let overweight mail slide. Here's what happens:

Scenario 1: Return to Sender

If you have a return address, USPS returns the letter to you stamped "Insufficient Postage" or "Returned for Additional Postage." You'll need to add the correct postage and re-mail it.

Scenario 2: Postage Due

If there's no return address — or USPS decides to deliver anyway — the recipient may be required to pay the difference before receiving it. This is awkward if you're mailing important documents, invoices, or legal notices.

Scenario 3: Delayed or Lost in Transit

Sometimes underweight mail gets stuck in processing limbo, especially if it's flagged as non-machinable or improperly sorted. Delays of 1-2 weeks aren't uncommon.

⚠️ Pro Tip

If your letter weighs 0.95-1.0 oz or more on a home scale, add an additional ounce stamp. It costs $0.29 and prevents a returned letter worth far more in time and hassle.

How to Calculate Postage for Heavier Letters

USPS First-Class Mail pricing increases in 1-ounce increments up to 3.5 oz. After that, you'll need to use a different mail class or visit a post office.

Weight Range	Postage Required	Total Cost
Up to 1 oz	1 Forever Stamp	$0.78
1-2 oz	1 Forever + 1 additional oz ($0.29)	$1.07
2-3 oz	1 Forever + 2 additional oz ($0.58)	$1.36
3-3.5 oz	1 Forever + 3 additional oz ($0.87)	$1.65

Note: Letters over 3.5 oz must be sent as a large envelope (flat) or package, with pricing starting around $1.63 for the first ounce.

Can You Use Multiple Forever Stamps Instead?

Yes — but it's more expensive. Two Forever Stamps = $1.56, while the correct postage for a 2 oz letter is only $1.07. You're overpaying by nearly 50 cents per letter.

If you mail frequently, buy additional ounce stamps (often sold at post offices in sheets of 20) and use them alongside Forever Stamps.

How to Weigh Your Mail at Home

The easiest way to avoid postage issues is to weigh your letter before mailing. Here's how:

Option 1: Digital Postal Scale

Postal scales (available for $15-30) are accurate to 0.1 oz and measure up to 5-10 lbs. They're worth the investment if you mail regularly.

Option 2: Kitchen Scale

Most digital kitchen scales work fine for letters, as long as they measure in ounces (not just grams or pounds). Place your sealed envelope on the scale and check the weight.

Option 3: Post Office Scale

Every USPS retail counter has a scale. If you're unsure, bring your letter unsealed to the post office, have them weigh it, and pay the exact postage. They'll also hand-cancel it to prevent damage in automated sorting.

💡 Digital Alternative

Want to skip the post office entirely? Mail your letter online — upload your document, and we'll print, stamp, and mail it with the correct postage automatically.

Special Cases: When Weight Limits Get Tricky

Greeting Cards and Invitations

Most standard greeting cards stay under 1 oz and qualify for a single Forever Stamp. However, cards with:

Metallic or glitter embellishments
Thick embossed designs
Multiple inserts or photos
Rigid or square envelopes

...may require a non-machinable surcharge ($0.48 extra) even if they're under 1 oz, because they can't run through automated sorting machines.

Legal and Certified Mail

If you're mailing legal documents via Certified Mail, the weight limit still applies. Certified Mail is an add-on service (currently $5.3), not a replacement for postage. You still need a Forever Stamp (or correct postage) plus the Certified Mail fee.

International Mail

Forever Stamps do not work for international mail. You'll need an international Forever Stamp (currently $1.7) or country-specific postage. Weight limits differ by destination.

Common Mistakes to Avoid

❌ Assuming 6-10 sheets = 1 oz. Most 6+ sheet letters exceed 1 oz. Weigh it.
❌ Using Forever Stamps for large envelopes. A 9×12 envelope requires flat-rate postage, not letter-rate stamps.
❌ Skipping the scale for "important" mail. Legal notices, invoices, and contracts with insufficient postage get returned just like any other mail.
❌ Trusting old postal guides. Rates and rules change. Always check current USPS standards.

Quick Checklist: Is Your Letter Good to Go?

Before you drop your letter in the mailbox:

✅ Letter weighs 1.0 oz or less (use a scale)
✅ Envelope is within 11.5" × 6.125" × 0.25" size limits
✅ Envelope is flexible and rectangular (not rigid or square)
✅ You've added extra postage if needed (additional ounce stamps)
✅ Return address is clearly written in case of return

Bottom Line

A Forever Stamp covers letters up to 1 ounce — no exceptions. If you're mailing anything heavier, add an additional ounce stamp for every ounce over 1 oz, or visit a post office to pay the exact rate.

The cost difference is small (29 cents per ounce), but the hassle of returned mail is huge. When in doubt, add extra postage or use an online mailing service that calculates postage automatically.