Ever stood in line at the post office, unsure if your package will fit the right box or how much it’ll cost to send? You’re not alone—figuring out USPS package sizes can be confusing, but it’s crucial for saving money, avoiding delays, and ensuring your item arrives safely.
This article breaks down how USPS defines different package sizes, explains which dimensions matter, and offers tips for measuring your parcel to keep your shipping hassle-free.
Understanding USPS Package Sizes: A Complete Guide
When you send a package with USPS, knowing the rules about package sizes is crucial. It affects not just whether your item can be shipped or not, but also how much you’ll pay. In this guide, you’ll discover the ins and outs of USPS package sizes, how they are measured, what limits apply, and how to optimize your shipping for cost and convenience.
USPS Package Size Basics
What Is a USPS Package Size?
USPS refers to any box, envelope, or tube used for shipping as a “package” or “parcel.” USPS separates packages by size, weight, and shape, and has specific restrictions you need to know:
- Minimum Size: The smallest item must be at least 6 inches long, 3 inches high, and 1/4 inch thick.
- Maximum Size: For most USPS services, the largest allowed package cannot exceed 108 inches in combined length and girth.
- Oversized Packages: Some services (like USPS Retail Ground) allow parcels up to 130 inches in length plus girth, but higher fees apply.
Key USPS Package Size Limits by Service
USPS offers a variety of shipping services, and each has its own size guidelines:
- First-Class Package Service
- Max weight: 15.999 ounces
- Max size: 22” x 18” x 15”
- Priority Mail and Priority Mail Express
- Max weight: 70 lbs
- Max size: 108 inches in combined length and girth
- USPS Retail Ground/Parcel Select
- Max weight: 70 lbs
- Max size: 130 inches in length plus girth
Length: The longest side of the parcel.
Girth: The distance all the way around the thickest part (not including the length).
To calculate:
Girth = 2 x (Width + Height)
Measuring Your USPS Package: Step-by-Step
Getting your measurements right is crucial to avoid extra charges or rejected parcels. Here’s how to do it:
- Measure the Length: Use a measuring tape or ruler. Measure the longest side of your package.
- Measure the Width: This is the side perpendicular to length.
- Measure the Height: Stand the parcel up and measure the remaining dimension.
- Calculate Girth: Add the width and the height together, multiply by two.
(e.g., 8″ width + 6″ height = 14″ x 2 = 28″ girth) - Add Length + Girth: This is your total USPS package size.
Example Calculation
- Box dimensions: 20″ (L) x 10″ (W) x 5″ (H)
- Girth: 2 x (10 + 5) = 2 x 15 = 30″
- Length + Girth: 20 + 30 = 50″
- This is within standard size limits.
Benefits and Challenges of USPS Size Standards
Benefits
- Efficiency: Standard sizes help USPS process and transport packages quickly.
- Predictable Costs: Knowing maximum sizes allows you to estimate postage more accurately.
- Variety: USPS offers diverse options for small, medium, and large packages.
Challenges
- Oversized Fees: Exceeding standard sizes can lead to higher charges.
- Rejected Packages: Packages too small or too big might not be accepted.
- Dimensional Weight Pricing: For large but lightweight parcels, shipping may be priced by “dimensional weight” instead of actual weight.
Dimensional Weight: What You Need to Know
Dimensional weight pricing means you’re charged for the space your package occupies, not just its physical weight. This applies mainly to larger packages shipped via Priority Mail and Priority Mail Express.
How it works:
- USPS calculates the dimensional (DIM) weight:
(Length x Width x Height) ÷ 166 - If DIM weight is more than the actual weight, you’ll pay the higher amount.
Tip: Use appropriately sized packaging—don’t ship small items in large boxes.
Common USPS Package Types
Understanding common packaging helps choose the right size for your needs:
- Letters: Must be at least 3.5″ x 5″ and not more than 6.125″ x 11.5″
- Large Envelopes (Flats): Min: 6.125″ x 11.5″, Max: 12″ x 15″
- Parcels: Any box, thick envelope, or tube not qualifying as a letter or flat
Popular Package Categories
- Small Packages: Books, small electronics, apparel (use First-Class or Small Flat Rate Box)
- Medium Packages: Shoes, larger electronics, toys (Priority Mail Medium Flat Rate Box)
- Large Packages: Bulkier household goods, sports equipment (Priority Mail Large Flat Rate Box or Retail Ground)
Practical Tips for Shipping with USPS
1. Choose the Smallest Suitable Package
The smaller and lighter your parcel, the less expensive your shipping cost.
2. Verify Minimum and Maximum Sizes
If your package is below minimum USPS size, you’ll need to place it in a larger envelope or box.
3. Use USPS Flat Rate Options
“Flat Rate Boxes” let you fit as much as you can (up to 70 lbs), for one set price—ideal if size/weight varies but stays within limits.
4. Weigh and Measure Carefully
Accurate measurements prevent surprise fees. Use a tape measure and digital scale.
5. Print Labels Online
USPS online shipping tools walk you through the correct measurements and instantly show postage costs.
6. Keep Packaging Durable
Avoid overstuffing boxes and use strong packing tape. Flimsy or irregular parcels can get damaged or separated during transit.
USPS Size and Shipping Cost Tips
- Compare Pricing: Use the USPS postage calculator to test different package sizes and services to find the best value.
- Check Dimensional Weight Thresholds: Especially if you’re shipping large but lightweight boxes. Sometimes splitting contents into smaller boxes saves money.
- Flat Rate Boxes for Heavy Items: These often save money if you’re shipping something dense, as long as it fits in the box.
- Reuse Boxes Carefully: Ensure reused boxes meet USPS size and strength standards—remove any old labels and barcodes.
- Know Surcharges: Oversized or non-standard items (like tubes or odd shapes) may incur extra fees.
Best Practices for Smooth USPS Shipping
- Label Clearly: Ensure your address label is legible and firmly attached.
- Secure Contents: Use padding and bubble wrap to prevent movement inside the box.
- Seal All Openings: Use approved tape—avoid strings or wrapping paper.
- Avoid Prohibited Items: Always check USPS guidelines for restricted contents.
- Include a Return Address: This helps return your package if delivery fails.
Final Summary
Shipping with USPS is straightforward once you know the package size rules. Always measure your boxes, choose the smallest practical option, and be aware of dimensional weight charges. Using USPS Flat Rate options can simplify costs, especially for heavier items. Following these tips ensures your packages get to their destination efficiently, safely, and affordably.
Frequently Asked Questions (FAQs)
1. What is the largest package size USPS will accept?
USPS accepts packages up to 108 inches in combined length and girth for most services. For USPS Retail Ground and Parcel Select, the maximum is 130 inches.
2. Is there a minimum size for shipping with USPS?
Yes, the minimum size for parcels is 6 inches long, 3 inches high, and 1/4 inch thick. Anything smaller needs to be placed in a larger envelope or box.
3. Does USPS charge by weight or size?
USPS charges by actual weight in most cases. However, for larger (but lightweight) packages, dimensional weight pricing may apply—especially for Priority Mail and Express services.
4. How do I measure length and girth for USPS packages?
Measure the longest side for the length. To find girth, add the width and height, then multiply the sum by two. Add length and girth to get your total USPS package size.
5. What happens if my package is too large for USPS?
If your parcel exceeds the maximum allowed size, USPS will not ship it, and you may need to use a different carrier or separate your shipment into smaller packages.
