How Many Forever Stamps Do I Need? (Letters, Large Envelopes & Packages)

Quick Answer: How Many Forever Stamps Do I Need?

One Forever stamp covers a standard one-ounce letter. For anything heavier or unusually shaped, you need more postage. This chart uses the current USPS rates that took effect July 12, 2026 (one Forever stamp = $0.82 of postage):

Your Mailpiece	2026 Postage	Forever Stamps Needed
Standard letter, up to 1 oz	$0.82	1 stamp
Letter, up to 2 oz	$1.11	2 stamps
Letter, up to 3 oz	$1.40	2 stamps
Letter, up to 3.5 oz (max)	$1.69	3 stamps
Square or oversized envelope	from $1.31	2 stamps
Large envelope (flat), 1 oz	from $1.69	3 stamps
Postcard (standard size)	$0.65	1 stamp (or a Postcard stamp)
International letter, 1 oz	$1.75	Global Forever (or 3 stamps)

Buying postage at the post office costs full price. You can also buy genuine, new Forever stamps below face value — more on that at the end.

The Basic Rule: One Stamp = One Ounce

A Forever stamp always covers whatever the current one-ounce First-Class letter rate is — today that is $0.82, and it will still be enough after future price increases. That is the whole point of “Forever.”

Standard letters are rectangular, flexible, and at least 6¼” × 3½”. If your envelope fits that description and weighs an ounce or less (about 4 sheets of paper plus the envelope), one Forever stamp is all you need.

How to Calculate Stamps for Any Letter (Simple Math)

Divide the total postage by $0.82 and round up. That’s the entire formula.

USPS adds $0.29 for each additional ounce (or fraction of an ounce) on letters, up to the 3.5 oz letter maximum:

• 2 oz letter: $0.82 + $0.29 = $1.11 → $1.11 ÷ $0.82 = 1.35 → 2 Forever stamps
• 3 oz letter: $0.82 + ($0.29 × 2) = $1.40 → 2 Forever stamps ($1.64 of postage — you overpay slightly)
• 3.5 oz letter: $1.69 → 3 Forever stamps

Yes, combining Forever stamps sometimes means paying a few cents more than the exact rate. USPS does not issue change, but it does accept overpayment. Underpaying is the bigger problem: short-paid mail gets returned or delivered with postage due, which delays your letter by days.

Square, Oversized, and Unusual Envelopes: $1.31 and Up

Square envelopes and unusually shaped mail start at $1.31 — the “nonmachinable” surcharge — even if they weigh less than an ounce. That means 2 Forever stamps ($1.64) for a typical square greeting card or invitation.

This matters most for weddings: most invitation suites are square or lumpy (ribbons, wax seals, multiple cards). Before buying postage for 100 invitations, take one finished suite to a post office and have it weighed and measured. Then stock up on wedding stamps in bulk so every invitation is covered.

Large Envelopes (Flats): 3 Stamps to Start

A 1 oz large envelope (flat) starts at $1.69, so you need 3 Forever stamps. Each additional ounce adds $0.29. Flats are the big envelopes you use for documents, manuscripts, and magazines — up to 15″ × 12″ and 13 oz max.

Postcards: Cheaper Than a Forever Stamp

Standard postcards cost $0.65 to mail, so one Forever stamp works (you overpay 17¢). If you mail postcards often, Postcard stamps cost exactly $0.65 and avoid the overpayment. Oversized postcards, however, are charged letter rates — $0.82 and up.

International Mail: Use Global Forever Stamps

A 1 oz letter to any country costs $1.75. The clean solution is a Global Forever stamp (currently $1.75 — round, shows different designs). Three regular Forever stamps also technically cover it, but you’d overpay 71¢ per letter, which adds up fast if you mail internationally often.

Packages: Don’t Use Stamps

Anything over 13 oz, or thick/rigid enough to be a package, ships as a package — USPS Ground Advantage or Priority Mail. You can cover a package entirely in stamps, but it is impractical. Package postage is weight- and distance-based; use Click-N-Ship or a post office counter and save your Forever stamps for letters and flats.

Common Stamp Mistakes (And What They Cost You)

• Assuming old rates. Prices rose to $0.82 on July 12, 2026 (from $0.78). Mail sent with correct-for-2025 postage on a 1 oz letter is now 4¢ short.
• Guessing weight. A kitchen scale accurate to 0.1 oz costs less than one returned letter. Four sheets of 20 lb paper + envelope ≈ 1 oz; ten sheets ≈ 2 oz.
• Ignoring shape. A 1 oz square envelope needs $1.31, not $0.82. Shape triggers surcharges before weight does.
• Overpaying “to be safe.” Extra stamps are wasted money — USPS keeps the difference.

The Smart Way to Buy Forever Stamps: Below Face Value

Every rate in this article is what you pay at retail. But postage works like any commodity: when businesses buy in bulk and resell, genuine Forever stamps trade below face value.

At US Stamps Deals, every stamp is genuine USPS-issued postage — new, unused, and verified against the official USPS issue record. Sheets bring the per-stamp cost down to around 25¢, and wholesale rolls take it lower still. That means the $0.82 letter you just calculated can actually cost you a fraction of that to mail.

Because Forever stamps never expire, buying ahead at a discount locks in savings through every future rate hike. Want the full picture of how Forever stamps hold value? Read our complete Forever stamps guide.

FAQ

Rates in this article: USPS First-Class Mail prices effective July 12, 2026; verified October 2026. See usps.com for the official current price list.