How Many Stamps Do I Need for 3oz?


March 10, 2024

The concept of postage stamps seems pretty straightforward. At its core, you purchase a stamp, carefully affix it onto your letter or package, and your shipment is ready to journey to its intended destination.

This practice has existed for well over a century since it was introduced by the United States Postal Service (USPS), and it’s become an integral part of many Americans’ daily lives. However, like many seemingly simple processes, the details can be complicated.

The complexity of postage stamps is evident when you try to answer the seemingly fundamental question, “How many of these small, adhesive pieces of paper do I need to ensure my mail reaches its destination without hiccups?”

Determining the number of stamps required for your mail isn’t a one-size-fits-all scenario. Various factors influence the answer, from the shipping cost to the postage denomination you use.

This article will help you navigate the intricacies of postage stamps and postage rates. If you need additional information on USPS postage, visit your local post office. Find your area’s nearest and most convenient USPS facilities among the over 31,000 nationwide with

About Postage Stamps

Before we dive into the specifics of how many stamps you need for different weights and types of mail, let’s start with a quick overview of postage stamps.

Postage stamps are little, sticky squares issued by the United States Postal Service, also known as the U.S. Mail service or simply USPS. The primary purpose of these pieces of paper is to indicate the amount of postage you paid.

Kinds of Postage Available in the Market

USPS offers a variety of postage options to cater to different mailing requirements. From specialty stamps, like the Forever stamp, to denominated stamps, there’s a postage solution for everyone.

Here are some of the most common postage stamp types and their prices as of September 2023:

  • First-Class Mail One-Ounce Price Forever stamps: Regardless of any future price changes, a First-Class Mail One-Ounce Price Forever stamp always has the same value as the shipping cost for a 1 oz letter via First-Class Mail. The postage price is $0.66.
  • First-Class Mail Additional Ounce Forever stamps: Each of these adhesive stamps covers the cost of extra ounces beyond First-Class Mail’s first-ounce price. The cost of an Additional Ounce Forever stamp is $0.24.
  • First-Class Mail Presorted stamps: These stamps are typically used for commercial mail, such as Marketing Mail, and are available if you have a mailing permit and a Business Mail Entry (BME) induction.
  • Postcard stamps: Like Forever stamps, postcard stamps simplify postage calculation by providing a one-stamp solution for sending postcards. The value of each of these stamps is $0.51.
  • Denominated stamps: These stamps generally range between 1¢ to $25.00 and are worth the value printed on their face. Denomination or definitive stamps include Priority Mail and Priority Mail Express stamps.

How Many Stamps Do I Need per Oz?

Determining the number of stamps you must attach to a letter or package to cover the shipping cost depends on several factors, including the weight, size, destination, and the type of mail you’re sending.

Let’s break it down by ounces to make it easier to understand.

How Many Stamps Do You Need to Use for a 1oz Letter?

As mentioned, the U.S. Postal Service’s Forever stamp value is always equivalent to the current First-Class Mail postage rate. So when sending a 1-ounce letter via the First-Class Mail service, which costs $0.66, you only need to use one Forever stamp.

How Many Stamps Do You Need to Use for a 1.5oz Letter?

If your letter weighs 1.5oz, you’ll need more than one stamp. In this case, you can use one First-Class stamp for the first ounce and add an Additional Ounce stamp for the extra 0.5 ounce ($0.66 + $0.24 = $0.90).

However, since half an ounce is only $0.12, using this combination means paying $0.12 more. 

You can pay the exact price using a 12-cent stamp or a variety of denominated stamps worth $0.12 plus one Forever stamp ($0.66 + $0.12 = $0.78).

How Many Stamps Do I Need for 2oz?

The postage fee to send a two-ounce First-Class Mail letter is $0.90. To cover the shipping cost, you can use a Forever or First-Class stamp for the first ounce and an Additional Ounce stamp for the second ounce ($0.66 + $0.24 = $0.90).

How Many Stamps Do I Need for 3oz Packages?

There are various options to consider when sending a three-ounce mailpiece, depending on the type of First-Class package you’re sending.

How Many Stamps Do I Need for a 3oz letter?

As of September 2023’s postage rate, shipping a letter weighing 3oz via First-Class Mial costs $1.14. You can use one First-Class stamp to cover the first ounce and two Additional Ounce stamps for the extra two ounces ($0.66 + [$0.24 x 2] = $1.14).

How Much Postage Do I Need for a 3oz Flat?

For the U.S. Postal Service, “flats” refer to large envelopes that have a dimension of around 6 ⅛” high, 11 ½” long, and ¼” thick but don’t exceed 12” tall, 15” long, and ¾” thick.

The postage rate for mailing a 3oz flat, as of September 2023, is $1.83. In this scenario, you can use three Forever stamps ($0.66 x 3 = $1.98), but you’ll pay $0.15 more.

To pay the exact price, you can use two Forever stamps, two Additional Ounce stamps, and a three-cent stamp ([$0.66 x 2] + [$0.24 x 2] + $0.03 = $1.83).

How Many Stamps Do I Need for a 3oz Bubble Mailer?

You can send bubble-lined envelopes through First-Class Mail if they meet the size restrictions. Small bubble mailers, 8 ½ inches high and 12 inches long, still qualify as flats.

A 3oz bubble mailer costs $0.84 to ship. You can use a combination of a Forever stamp plus denomination stamps equal to $0.18 ($0.66 + $0.18 = $0.84) to cover the postage cost.

How Many Stamps Do I Need for 3.5oz?

The September 2023 postage rate to send a First-Class Mail letter weighing 3.5oz is $1.38. In this case, you’ll want to use one First-Class stamp for the first ounce and add three Additional Ounce stamps to cover the remaining weight ($0.66 + [$0.24 x 3] = $1.38).

How Many Stamps Do I Need for a Large Envelope (Flats)?

Sending letters via large envelopes or flats follows a similar pattern. The number of stamps needed depends on the weight of your mail.

How Many Stamps Do You Need to Use for a 4oz Letter?

You must pay $2.07 to ship a four-ounce letter via First-Class Mail. To cover the entire postage fee, use three First-Class stamps plus denominated stamps worth $0.09 ([$0.66 x 3] + $0.09 = $2.07).

How Many Stamps Do You Need to Use for a 5oz Letter?

A 5-ounce letter requires a $2.31 postage. To cover the shipping cost precisely, use three Forever stamps, an Additional Ounce stamp, and a 9¢ denominated stamp ([$0.66 x 3] + $0.24 + $0.09 = $2.31).

How Many Stamps Do You Need to Use for a 6oz Letter?

Are you sending a 6-ounce letter? If so, the postage cost is $2.55. In this scenario, you’ll want to use three First-Class stamps, two Additional Ounce stamps, and a 9¢ denominated stamp ([$0.66 x 3] + [$0.24 x 2] + $0.09 = $2.55.

How Many Stamps Do You Need to Use for a 7oz Letter?

For a 7-ounce letter, which costs $2.79 to mail, use four Forever stamps and a definitive stamp valued at $0.15 ([$0.66 x 4] + $0.15 = $2.79).

How Many Stamps Do You Need to Use for an 8oz Letter?

To send an 8-ounce letter, you’ll need a stamp or a combination of stamps equal to $3.03. An exact combination consists of four Forever stamps, an Additional Ounce stamp, and a 15¢ denomination stamp ([$0.66 x 4] + $0.24 + $0.15 = $3.03).

How Many Stamps Do You Need to Use for a 9oz Letter?

For a 9-ounce letter, you’ll need to cover a postage rate of $3.27. You can achieve this value using four First-Class stamps, plus two Additional Ounce stamps, and definitive stamps equal $0.15 ([$0.66 x 4] + [$0.24 x 2] + $0.15 = $3.27).

How Many Stamps Do You Need to Use for a 10oz Letter?

A 10-ounce letter requires five Forever stamps and an Additional Ounce stamp ([$0.66 x 5] + $0.24 = $3.54). This combination of postage stamps covers the shipping cost of mailing a 10oz letter, but you’ll be paying $0.03 more. 

To avoid overpaying, you can use five First-Class stamps and a combination of denominated stamps worth $0.21 ([$0.66 x 5] + $0.21 = $3.51).

How Many Stamps Do You Need to Use for an 11oz Letter?

If your letter weighs 11 ounces, the postage rate is $3.75. To cover this cost, use five Forever stamps, an Additional Ounce stamp, plus a combination of definitive stamps equal $0.21 ([$0.66 x 5] + $0.24 + $0.21 = $3.75).

How Many Stamps Do You Need to Use for a 12oz Letter?

Sending a 12-ounce letter via First-Class Mail will cost you $3.99. In this scenario, you can use six Forever stamps and a three-cent stamp to cover the postage cost ([$0.66 x 6] + $0.03 = $3.99).

How Many Stamps Do You Need to Use for a 13oz Letter?

The heaviest flat you can send via the U.S. Postal Service’s First-Class Mail option is 13oz. It costs $4.23 to mail a letter at this weight and will require you to use six Forever stamps, an Additional Ounce stamp, and a 3¢ denomination stamp ([$0.66 x 6] + $0.24 + $0.03 = $4.23).

Envelope Requirements

The maximum weight of an envelope you can ship via the First-Class Mail service is 13oz. As mentioned, the size of the envelope also cannot exceed 12 inches high, 15 inches long, and ¾ inch thick. 

Additionally, if your envelopes aren’t uniformly thick or have an irregular shape, you’ll incur additional postage fees known as nonmachinable surcharges. This extra postage will cost you an additional $0.40.

Note that if your mailpiece exceeds the weight and size restrictions of First-Class Mail, you must pay the package rates of USPS Ground Advantage. In other words, you must now consider the parcel’s destination in the postage price calculation.

How Many Stamps to Send a Parcel to the USA?

The abovementioned computation applies when sending domestic letters and packages within the USA. However, if you’re sending a parcel that exceeds the standard size and weight limits of First-Class Mail, you may need to use other USPS postage options like Priority Mail.

The main benefit of using Priority Mail and its expedited variant, Priority Mail Express, is that you can use flat-rate packaging. These flat-rate envelopes and boxes allow you to send packages up to a specific weight anywhere in the country at the same price.

For more information on the postage costs of other Postal Service mail deliveries, visit the USPS website at Alternatively, you can contact a Postal worker at a post office location. Quickly find USPS facilities with’s locator tool.

How Many Stamps When Sending a Letter to Mexico?

Like sending a First-Class Mail letter within the U.S., the number of stamps you need when mailing to Mexico varies depending on the mailpiece’s weight and size.

Fortunately, you can use domestic Forever stamps to ship a letter to an international address like Mexico, and the same stamp-counting principle applies.

However, determining the appropriate number of stamps can be complex because a one-ounce letter costs $1.50, and a domestic Forever stamp is only worth $0.66.

Fortunately, the U.S. Postal Service has an answer- Global Forever stamps. These postage stamps’ value is tied to the shipping cost of sending a 1oz letter via First-Class Mail International, which is $1.50.

How Many Stamps to Send Deliveries to the U.K.?

USPS assigns each country to a price group, determining the cost of sending mail to that location. Under this system, the United Kingdom of Great Britain and Northern Ireland is part of First-Class Mail International’s price group 5.

If you’re sending a 1oz letter, you must cover the $1.50 shipping cost, which requires one Global Forever stamp. For a two-ounce letter, you need a combination of stamps worth $2.80.

In this scenario, you can use one Global Forever stamp, five Additional Ounce stamps, and a 10¢ definitive stamp ($1.50 + [$0.24 x 5] + $0.10 = $2.80).

Sending Deliveries to Canada

Like other international addresses, the cost of mailing a letter to Canada is subject to the parcel’s weight and size. Sending a mailpiece weighing 3.5oz, for instance, costs $2.75. 

This postage rate requires you to use one Global Forever stamp, five Additional Ounce stamps, plus a 5¢ denominated stamp ($1.50 + [$0.24 x 5] + $0.05 = $2.75).

How Many First-Class Postage Required?

First-Class or Forever postage is an excellent choice for mailing letters and postcards, as these stamps’ value remains constant even as postage rates change. As mentioned, you must consider the weight and size of your mail to determine the number of stamps needed.

How Many Stamps for a Postcard?

If you’re sending a postcard via First-Class Mail, determining the number of postage stamps you need is simple – one for each postcard you send. The U.S. Postal Service offers stamps explicitly designed for postcards, valued at $0.51 as of September 2023.

However, for your mailpiece to qualify as a “postcard,” it must be at least 3 ½” high, 5” long, and 0.007” thick. It must also not be more than 4 ¼” high, 6” long, and 0.016” thick.

The Easiest Way to Know How Many Stamps You’ll Need

Calculating postage for standard letters can sometimes be a math puzzle. However, USPS provides a handy online postage price calculator on its website, making it easier to determine if you have enough stamps for your mail.

Calculating Postage at the Post Office

If you’re unsure about the postage cost for your package, the best thing to do is to visit your local post office, hand your mailpiece to a Postal Service representative, and tell them what shipping service to use.

By doing so, USPS can weigh your letter or package, sell you the appropriate amount of postage stamps, and assist you if you have any further inquiries, such as how to apply the stamps to your parcel.

To find your area’s nearest and most convenient post office locations quickly, visit and use the USPS facility finder tool.

Where to Buy the Stamps You Need and the Postage Costs

Now that you know how many stamps you need, you’ll want to know where and how much they cost. Fortunately, you have various options, from online retailers like Amazon to pharmacies like CVS and financial institutions.  


Based on USPS’ September 2023 postage rates, here’s the cost of a stamp for the following mail items:

First-Class Mail Letter (First ounce)$0.66
First-Class Mail Letter Additional Ounce$0.24
Flats/Large Envelope (First ounce)$1.35
Flats/Large Envelope Additional Ounce$0.24

Flat-Rate Envelopes

Using flat-rate envelopes can be cost-effective for sending mail exceeding the weight and size restrictions of First-Class Mail. As of September 2023, here’s the prices for the various flat-rate envelope types:

Priority Mail Flat Rate Envelope$9.65
Priority Mail Legal Flat Rate Envelope$9.95
Priority Mail Padded Flat Rate Envelope$10.40
Priority Mail Express Flat Rate Envelope$28.75
Priority Mail Express Legal Flat Rate Envelope$28.95
Priority Mail Express Padded Flat Rate Envelope$29.45

International Mail and Packages

If you’re sending international mail or packages, you can use Global Forever stamps, specially designed for First-Class Mail International. Be aware that international shipping rates can vary widely depending on the destination.

Nonetheless, here’s the September 2023 postage pricing for the following:

First-Class Mail International Letter (First ounce)$1.50
First-Class Mail International Flats/Large Envelope (First ounce)$3.00

How Much Does a Stamp Cost?

Note that the postage rates discussed in this article are based on USPS’ September 2023 price list. Understanding that the U.S. Postal Service updates its postage fees periodically is essential.

To show you how frequent these price changes are, here are some of the previous USPS postage cost amendments:

New Prices Effective July 10, 2022

On July 9, 2022, the Postal Regulatory Commission (PRC) announced a two-cent price increase for First-Class Mail, raising the postage cost from $0.58 to $0.60. This change took effect the following day, July 10, 2022.

Previous Price Increases

The most recent postal price increase occurred on July 9, 2023. This change also increased the price of First-Class Mail and, by extension, the price of a Forever stamp from $0.63 to $0.66.

Staying current on USPS services’ price changes is crucial. To stay informed, visit the USPS website at or contact the USPS customer service hotline at 1-800-ASK-USPS (1-800-275-8777).

Conversely, you can contact a postal worker at your local post office. You can easily find USPS facilities using’s locator tool.

Additional Services Rates

The U.S. Postal Service offers add-on services to add a layer of security to your shipments. These extra services include return receipts, certificates of mailing, and insurance. However, including these services in your mailpiece will increase the postage costs.

Here’s a look at the September 20203 additional service rates:

Certified Mail$4.35
Certificate of Mailing$1.95
Return Receipt$3.55 (Hard copy PS Form 3811, Domestic Return Receipt)$2.20 (Electronic)
Insured MailStarts at $2.70
Registered MailStarts at $16.80

Easy Rules for Calculating Postage

Understanding how to calculate the required number of stamps for your mail is essential, and it depends on several pivotal factors, including the following:

  • Type of envelope: The envelope you plan to send is critical in determining the postage needed. As mentioned, exceeding envelope size requirements may force you to pay package rates and impact the total cost of postage.
  • Weight of the contents: The weight of the items within your envelope is the most significant factor affecting postage calculations.

To explain, a Forever stamp is sufficient to send a one-ounce envelope anywhere within the United States. However, as your letter becomes heavier, additional postage becomes necessary.

  • Destination: While the weight of the letter or package is the primary influencer of domestic postage pricing, the destination or country price group is a consideration for international mail. In short, mailpieces destined overseas require additional postage.

Weighing Your Mail to Figure Out Postage

A one-ounce difference can mean the difference between paying flat postage and package prices and sticking additional stamps on your mailpiece. Therefore, it’s essential to ensure you weigh your letters and packages accurately.

How to Weigh Your Envelope

Consider buying a postage scale. This tool helps ensure your envelope meets the U.S. Postal Service’s shipping guidelines. You can purchase postal scales at post offices, the USPS website, or a local office supply store.

Delivery Times for Letters to the United States

When sending letters within the United States via First-Class Mail, you can expect delivery within one to five business days. However, delivery time frames for international letters can vary, typically between 7 and 21 days.

COVID-19 / Coronavirus Status: Delivering Normally

During the COVID-19 outbreak and subsequent lockdowns, USPS experienced some disruptions in its on-time performance. However, as of September 2023, the U.S. Postal Service delivers mail as expected, with a 91.5% on-time delivery rate for First-Class Mail.

How Many Stamps Do I Need per Oz – FAQs

1. What happens if I don’t have the right amount of stamps?

If you don’t have the correct postage, USPS will, fortunately, still attempt to deliver your mail. However, the Postal Service will tag your letter or package as “Postage Due,” which will require the recipient to cover the insufficient postage.

Unfortunately, if the intended receiver doesn’t pay for the missing stamps, USPS may return the parcel or dispose of it if it doesn’t have a return address.

2. Where to apply stamps on a letter

According to the U.S. Postal Service’s guidelines on sending letters, you must place the stamps on the envelope’s upper right corner.

3. What does paper weigh?

The weight of paper can vary significantly, so choosing the appropriate paper type is essential when sending a letter, especially considering that heavier paper may require you to affix additional postage stamps. 

4. How many stamps are there in a pack?

A standard book of stamps typically includes 20 stamps. For your convenience, you can also purchase stamp coils or rolls containing 100 stamps.

5. How many stamps do I need for a postcard?

If your postcard meets the size requirement, which is below 4 ¼” high, 6” long, and 0.016” thick, you only need one Postcard stamp to send it.

 6. How many stamps do I need when sending a letter in the U.K.?

If you send a letter to the United Kingdom, the postage rate will depend on size and weight. For instance, a First-Class Mail International letter weighing 3oz requires $4.10 postage.

In other words, you can use two Global Forever stamps, four Additional Ounce stamps, and denominated stamps worth $0.14 ([$1.50 x 2] + [$0.24 x 4] + $0.14).

7. How many stamps do I need to send a parcel in the U.K.?

If you’re mailing a parcel using a large envelope or flat, prices start at $3.00. You can use two Global Forever stamps to cover the postage fee at this price point.

8. How many stamps do I need when mailing a 9×12 Manila envelope?

A 9×12 manila envelope still falls under the “flats” category. The number of stamps you must affix to this mailpiece will depend on its weight and destination.

For instance, shipping a 10oz manila envelope costs $3.51 to a domestic address. You must use five First-Class stamps and a $0.21 denominated stamp ([$0.66 x 5] + $0.21 = $3.51).

However, mailing a 4oz manila envelope to Canada means sticking a combination of postage stamps equal to $3.82. These assortments can include Global Forever, Additional Ounce, and definitive stamps.

9. Will three Forever stamps cover 3oz?

Whether three Forever stamps cover three ounces depends on what you’re sending and where. For example, three Forever stamps are sufficient for sending a 3oz standard letter domestically.

Standard letters are those that fit a No. 10 envelope. In other words, it has a minimum dimension of 3-1/2 inches high, 5 inches long, and 0.007 inches thick and doesn’t exceed 6-1/8 inches high, 11-1/2 inches long, and 1/4 inch thick. 

In this case, you’ll overpay $0.84, as three First-Class stamps equal $1.98, but the shipping cost to send a 3oz letter to a U.S. address is only $1.14.

However, if you’re sending a 3oz flat to a country in price group 5, such as the U.K., using three domestic Forever stamps won’t cover the postage cost of $5.45.

10. Can I mail a 3oz letter?

You can mail a three-ounce letter if you have the appropriate postage and meet USPS’ size guidelines. That said, while First-Class Mail is many individuals’ go-to letter delivery service, it isn’t the only U.S. Postal Service offering available.

For more information on USPS’ other reliable and cost-efficient letter-carrying options, talk to a Postal Service representative at a post office. Visit to find your area’s USPS facilities quickly.


  1. Postal history Stamps and postcards
  2. Postage Stamps – The Basics
  3. Forever Stamp Fact Sheet
  4. USPS Price List
  5. US Stamps by Denomination
  6. The Postal Store
  7. First-Class Mail
  8. Priority Mail Express
  9. Sizes for Postcards
  10. Where to buy postage stamps, including the post office, online, ATMs, and grocery stores
  11. July 2022 Postage Price Changes
  12. How Many Stamps Do I Need?
  13. Contact USPS
  14. First Class Package International Service
  15. Service Performance Remains Steady Across Postal Service Network
  16. What Happens if I Didn’t Put Enough Postage?
  17. How to Send a Letter or Postcard: Domestic
  18. How many stamps do I need? And where to buy?