How to Use the Stamps per Weight Calculator

A Stamps per Weight Calculator helps you determine how many standard postage stamps are needed to send a letter or small parcel based on its weight in ounces.

What It Does:

This calculator uses a simple rule: one USPS First-Class stamp covers up to 1 ounce of weight. If your mail weighs more than that, you’ll need additional stamps—typically one additional stamp per ounce or part of an ounce.

Steps to Use:

1. Enter the weight of your mail item in ounces (e.g., 3.5).
2. Click the “Calculate Stamps Needed” button.
3. The calculator will display:
   • The exact weight you entered.
   • The total number of stamps you need to affix.

The calculation uses round-up logic, meaning even if your letter is 2.1 oz, you’ll need 3 stamps.

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Stamps per Weight Calculator FAQ

Q1: How many ounces does one stamp cover?
A: One standard USPS First-Class stamp covers up to 1 ounce. For every additional ounce, another stamp is generally required.

Q2: Will this work for international mail?
A: No. This calculator is based on domestic First-Class letter rates in the U.S. International mail has different pricing and weight rules.

Q3: What if my letter is slightly over 1 ounce?
A: USPS requires you to round up. So even if it’s 1.1 oz, you'll need two stamps.

Q4: Can I use this for large envelopes or packages?
A: Not reliably. Large envelopes (flats) and packages have different rates. This tool is best for standard letters.

Q5: Is this an official USPS calculator?
A: No. This is an unofficial tool based on USPS guidelines for First-Class Mail. For exact pricing, visit usps.com.