How many stamps do I need? USPS stamp calculator (2026)
Free stamp calculator for domestic USPS First-Class mail—letters, large envelopes (flats), and common surcharges. Enter weight, dimensions, and handling flags to see totals aligned with March 2026 (verified) retail tables.
Postage depends on weight, dimensions, and how the piece moves through USPS equipment. Letters use a first-ounce rate (about $0.78 in 2026 here) plus $0.29 per additional ounce before surcharges. Large envelopes (flats) use a different retail table—if your mail is a flat, use the calculator below or the large envelope postage guide instead of letter stamp shortcuts. For common letter tiers, see 1 oz and 2 oz guides, or letter vs flat basics.
Last updated: April 17, 2026 · Rates from USPS Notice 123 figures (March 2026 (verified)) · Informational only; see USPS for official rules.
Quick answer: what this calculator estimates
For letters, postage is usually the first ounce plus each additional ounce, then any surcharges (for example non-machinable handling). For large envelopes (flats), USPS uses a different retail ounce table—your job is to get the classification right, then cover the dollar total. The tool below handles letter vs flat detection from your measurements (or you can force Letter / Large envelope / Flat modes).
Use the calculator: letters, flats, ounces & surcharges
This USPS postage calculator estimates domestic First-Class retail for letters and large envelopes (flats)—enter ounces, dimensions, mail class (Auto / Letter / Flat), and surcharge flags. For context on common big envelopes, see 9×12 envelope postage or the large envelope hub. International mail uses different products (FAQ below).
Stamps at a glance (standard letter)
Rounded to whole ounces; totals use current First-Class letter rates in this calculator.
- 1 oz → 1 stamp (1 Forever stamp) — $0.78 total
- 2 oz → 2 stamps (1 Forever + 1 additional ounce) — $1.07 total
- 3 oz → 3 stamps (1 Forever + 2 additional ounce) — $1.36 total
- Non-machinable (square, rigid, or lumpy) → + $0.49 surcharge on top of the ounce total
How many stamps do I need for a letter?
For USPS First-Class letters, postage is priced by billable ounces and the piece staying within letter size limits. A typical one-page letter in a standard #10 envelope is often 1 oz; add a page or a light enclosure and you may land on 2 oz. This stamp calculator turns that weight and envelope choice into a clear stamp count and dollar total using current retail logic—so “how many stamps do I need” becomes a number, not a chart hunt.
If you already know your ounce tier, start with the 1 oz letter postage or 2 oz letter postage guides for worked examples. For thicker mail, follow the 3 oz and 4 oz pages—each matches the same USPS stamps per ounce ladder you see here.
How the stamp calculator works
The tool is a structured USPS First-Class retail estimator: you enter weight and dimensions, choose Auto or force Letter / Large envelope (flat), and mark surcharges when they apply (for example non-machinable letter handling). Letters use the 2026 letter ounce ladder; flats use the large-envelope retail table—different products, both supported here.
What you get back
- Stamp-focused breakdown (Forever and additional-ounce stamps where that pairing fits common retail combinations)
- Total postage in dollars alongside stamp counts—useful when you are comparing convenience vs exact ounce pricing
- Plain-language flags when the piece may not be a standard letter (for example very large flats), so you do not mistake a flat for letter pricing
For preset scenarios, open 5×7 envelope postage, 6×9 envelope postage, or wedding invitation postage when thickness and presentation matter as much as weight.
When one stamp is not enough
A single Forever stamp covers the first ounce of a qualifying letter—but additional ounces need additional postage. That is why “one stamp” answers are only reliable when you are sure the piece is 1 oz and does not trigger shape or handling surcharges.
You may need more than the baseline stamp count when:
- Weight crosses into 2 oz, 3 oz, or up to 3.5 oz in the letter class—each step adds additional-ounce postage on top of the first ounce.
- Square or rigid mail behaves differently in automation—see square envelope postage and non-machinable mail for how surcharges stack with ounces.
- Large envelopes (flats) exceed letter dimensions or thickness limits; they use flat pricing, not the same Forever + additional-ounce letter ladder. If your piece reads as a flat, use 9×12 large envelope context and confirm dimensions at USPS.
USPS stamp rates (2026) used in this calculator
Figures below are retail-style First-Class letter components reflected in this site's March 2026 rate set (March 2026 (verified)). Always verify before high-value or time-sensitive mail—carriers update notices on usps.com.
- First ounce (letter): $0.78 base postage—commonly covered by a Forever-class stamp at retail
- Additional ounces (letter): $0.29 per extra ounce in the ladder used here
- Non-machinable surcharge (when applicable): $0.49 added on top of the ounce total for eligible letter pieces
- Standard postcard (single-piece retail reference): $0.61—see postcard postage 2026 for size rules vs letters
This presentation is informational, not an official USPS quote. For machine-readable price tables and international categories, refer to USPS Notice 123 and current Domestic Mail Manual guidance.
Letters, flats, postcards — pick the right lane
Use the calculator for your sealed piece, then open the guide that matches—letter ounces, a 9×12 flat, or a postcard. For a fast cross-check, see letter vs flat vs parcel or common postage mistakes.
- 1 oz and 2 oz letters: 1 oz and 2 oz guides walk through Forever + additional-ounce combinations.
- Heavier letters: 3 oz and 4 oz pages cover the upper end of many letter-class mailings.
- Large envelopes / flats: start with 9×12 envelope postage when you are clearly in flat territory.
- Postcards: compare retail postcard pricing and size rules on the 2026 postcard postage page—postcards are not priced like letters.
- International postage: outbound international mail uses different products; this calculator targets domestic letters— buy international postage from USPS for those sends (see FAQ).
Common mistakes (letters and flats)
- Guessing weight: even a few extra sheets can move a piece from 1 oz to 2 oz—use a kitchen scale or a Post Office scale when unsure.
- Ignoring shape: square envelopes and rigid cards can trigger surcharges even when weight looks light.
- Treating large envelopes like letters: big flats need flat postage; the ounce stamp ladder for letters does not transfer directly.
- International assumptions: outbound international mail uses different retail products and weight steps than domestic First-Class—this calculator targets domestic letter and flat retail estimates; buy international postage from USPS for those pieces.
When in doubt, confirm at retail or with official USPS tools. This site helps you plan totals and compare letter vs flat pricing—it does not replace clerk verification for unusual mail.
Frequently asked questions
Can I use multiple Forever stamps?
Yes. You can combine Forever stamps and other denominated USPS stamps so the total postage meets or exceeds the required amount for your letter's weight and surcharges. You may overpay slightly versus exact ounce retail if you only use large denominations—this calculator shows common Forever plus additional-ounce combinations when they fit.
What happens if my letter is overweight?
Mail that lacks sufficient postage may be returned, delayed, or handled as postage due depending on USPS processing—treat the risk as non-zero for important letters. Weigh the piece and add ounces on the First-Class letter ladder before mailing, or verify at retail.
Do square envelopes require extra postage?
Often yes—square letter mail can be non-machinable or otherwise subject to handling differences. Use the square envelope postage page and the calculator's surcharge options, then confirm unusual pieces with USPS.
How many stamps for international mail?
International postage uses different retail products and weight steps than domestic First-Class mail. This site's stamp calculator focuses on domestic letter and flat estimation—purchase international postage (stamp sheets, meters, or retail) from USPS international services for outbound international mail.
Does USPS round stamp weight up?
Yes. Letter postage in this calculator uses whole ounces on the rate ladder: fractional weight rounds up. A 1.2 oz piece is billed like 2 oz for retail letter pricing here.
How many stamps do I need for a 1 oz letter?
A qualifying 1 oz domestic First-Class letter typically needs postage equal to the first-ounce retail rate—often one Forever-class stamp for the first ounce in common retail combinations. Add surcharges if the piece is non-machinable or square per USPS rules; see the 1 oz letter stamp guide for examples.