How Many USPS Stamps Do I Need Per Ounce? (2025 Update)

USPS postage is based on weight and mail class. As of 2024/2025, mailing a standard U.S. letter up to 1 ounce requires one First-Class stamp (a “Forever” stamp worth 73¢). Each additional ounce adds 28¢ to the postage. Large envelopes (“flats”) start at $1.50 for the first ounce, and postcards require 56¢ postage (a postcard stamp) up to 1 oz. International letters and postcards up to 1 oz require a Global Forever stamp ($1.65). In practical terms:

Domestic Letters (First-Class Mail) – 1 oz costs 73¢. Use one Forever stamp (worth 73¢). For a 2‑ounce letter (1 oz + 1 oz), total postage is 73¢ + 28¢ = $1.01. You could use one Forever (73¢) plus a 28¢ stamp, or two Forever stamps (total 1.46) covering the $1.01 (the extra value is fine). In general, add 28¢ postage for each extra ounce.

Large Envelopes (Flats) – 1 oz is $1.50. You need postage totaling $1.50. For example, you could use a $1.50 large-envelope stamp if available, or two Forever stamps (1.46¢) plus a 4¢ stamp. Each additional ounce is 28¢, so a 2‑oz flat costs $1.78, etc.

Domestic Postcards – 1 oz postcard costs 56¢. Use a 56¢ postcard stamp or any combination totaling 56¢ (e.g., a 73¢ Forever stamp plus make up the difference if you have smaller stamps). If a postcard is over 1 oz or nonstandard size, it is treated as a letter (73¢ + 28¢/oz).

International Mail – Sending 1-oz letters or postcards abroad requires a Global Forever stamp (currently $1.65). Each country has its own extra-ounce rates for heavier letters; you would add additional Global stamps or extra postage for each ounce above 1 oz. (For example, 2 oz to most countries costs $2.20–$2.30 total.)

USPS Postage Rates (2023–2025)

Recent USPS rate changes (Approved by the Postal Regulatory Commission) have affected stamp prices:

- July 2024 – First-Class forever stamp rose from 68¢ to 73¢. Additional-ounce postage went from 24¢ to 28¢. Domestic postcard stamp became 56¢, and large flats increased from $1.39 to $1.50. Global Forever (international letter) rose to $1.65.

- January 2025 – No increase for mailing services; First-Class stamp remained 73¢. All domestic rates above stayed the same.

- July 2025 (proposed) – The Postal Service has proposed raising the First-Class stamp to 78¢ (additional ounce to 29¢, flats to $1.61, postcard to 62¢). These changes are pending approval and would take effect July 13, 2025.

In summary, as of 2024/2025: a 1‑ounce letter costs 73¢; each extra ounce adds 28¢. Flats start at $1.50, postcards at 56¢, and international letters at $1.65 (with Global Forever stamps). (Rates in 2023 were lower – e.g. 2023 first-class was 68¢ and add-oz 24¢ – but all current info is updated to 2024/2025.)

Forever Stamps vs. Denominated Stamps

Forever stamps are non-expiring stamps that always cover the current 1‑ounce First-Class letter rate. If you buy a Forever stamp today (73¢ value) and rates go up, that stamp still covers the new price. (For example, a Forever stamp bought at 68¢ still covered 73¢ after the 2024 increase.) Global Forever stamps work the same way for international 1‑oz letters (currently $1.65).

Denominated stamps, on the other hand, are fixed-value (like a 10¢ or 24¢ stamp) and do not change with rates. To use them, you must add up to the needed postage. In practice, most people use one or more Forever stamps plus add-on stamps (28¢, 44¢, etc.) for extra ounces.

Key point: Forever stamps simplify postage calculations for the first ounce. They never expire and always equal the current first-ounce rate. If you already have Forever stamps, you can use them even after a rate hike without needing more stamps, unlike old-valued stamps.

Using Stamps for Extra Ounces

If a letter or flat exceeds 1 oz, you pay for each additional ounce. Currently that’s 28¢ per ounce. For example:

- 2‑ounce letter: 73¢ + 28¢ = $1.01.

- 3‑ounce letter: 73¢ + 56¢ = $1.29.

- 2‑ounce flat: $1.50 + 28¢ = $1.78, etc.

Each extra ounce can be covered by stamps adding up to 28¢. USPS sells extra-ounce stamps (currently a 28¢ stamp) that you can add. You can also use an additional Forever stamp (adding 73¢) and have a credit of 45¢ on a 2‑ounce letter, which is allowed.

Remember, nonmachinable or oversized shapes incur surcharges; these may add extra postage beyond the normal rate (e.g. a 17¢ surcharge for a square envelope). For simplicity, follow USPS guidelines on size and weight or use their online postage price calculator or ask at the Post Office.

Tips & FAQ

Q: Can I use old Forever stamps? Yes – all Forever stamps are valid for the current postage. A Forever stamp bought years ago covers today’s 73¢ letter rate, and a global Forever always covers the current international 1-oz rate.

Q: What if my letter is over 1 oz? You must add postage. For each extra ounce, add 28¢ (e.g. one more Forever stamp plus a 45¢ “credit,” or one Forever + one 28¢ + one 17¢ stamp, etc.). USPS does not require exact postage, so a small overpayment is okay.

Q: How many stamps do I need for a 2‑ounce letter? Total postage is $1.01. You might use two 73¢ Forever stamps (total $1.46) and be 45¢ over, or one Forever (73¢) plus a 28¢ stamp. Either covers the cost.

Q: What if I only have Forever stamps and my letter is, say, 4 oz? 4‑ounce mail costs 73¢ + 3×28¢ = $1.57. You could use two Forever stamps ($1.46) plus a 11¢ stamp (for example). You cannot use only Forever stamps to exactly match $1.57, since each is 73¢. In practice, you often combine Forever + extra-ounce stamps.

Q: Do postcards need a special stamp? Yes, standard postcards need a 56¢ postcard stamp. If you put a 73¢ letter Forever stamp on a postcard, you’ll overpay. (You can use a Forever stamp + ask for 17¢ back at the counter, but it’s simpler to use the correct 56¢ stamp.) Oversize postcards count as envelopes.

Q: Do postage stamps expire? No, postage stamps never expire; even a 2¢ stamp from decades ago still has its face value in postage. Forever stamps similarly increase in value as rates rise.

Tip: Always weigh your mail (a kitchen scale works) and use the USPS online postage price calculator or ask at the Post Office. Rates change occasionally (recent hikes were in 2024 and a planned one in mid-2025), so check before mailing. Using Forever stamps and knowing the extra-ounce rate (28¢) is the easiest way to handle fluctuating rates.

Sources: Official USPS announcements and rate tables. All postage values are accurate as of 2025.