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Whether you’re shipping products nationwide as a small business owner or sending gifts to loved ones, choosing the right packaging and mailing option can save you time, money, and stress.
Overview of USPS Package Size Guidelines
USPS has specific size and weight limits for each shipping service. These guidelines ensure packages can be processed efficiently while helping customers avoid extra fees or delays.
When preparing a package:
- Measure the length: This is the longest side of the parcel.
- Calculate the girth: This is the distance around the thickest part, measured perpendicular to the length.
For certain services, especially larger parcels, USPS uses a combined length + girth threshold. Exceeding these thresholds can mean paying additional postage or using a different USPS service.
Understanding Length, Girth, and Dimensional Weight
Length
The length of a package is its longest dimension.
Girth
The girth is measured by wrapping a tape measure around the widest part of the package (perpendicular to length).
Girth = (Width * 2) + (Height * 2)
Dimensional Weight
Dimensional weight pricing applies when a box is large but the contents are relatively light (like shipping pillows or stuffed animals).
In these cases, USPS may charge according to an item’s volume rather than just its weight.
Key USPS Shipping Services
USPS offers several shipping services tailored to different needs. Each has its own size and weight guidelines:
USPS First-Class Package
- Best for lightweight packages up to 15.999 oz (commercial) or 13 oz (retail)
- Takes 1–5 business days for delivery
- Tracking can be included with First-Class Package Service
Because this service is designed for smaller parcels, the maximum combined length + girth is usually not the limiting factor; the weight (and sometimes dimensions) is more critical.
USPS Priority Mail
- Delivers in 1–3 business days
- Maximum weight: 70 lbs
- Includes free tracking and insurance up to $50 (or $100 for some commercial accounts)
- Offers Flat Rate and Regional Rate options that ignore distance (zones) if you use USPS-branded packaging
Priority Mail is ideal for both personal and business shippers who need faster delivery without the higher cost of Priority Mail Express.
USPS Priority Mail Express
- Fastest USPS shipping method, offering overnight or 1–2 day delivery
- Maximum weight: 70 lbs
- Includes tracking, plus insurance up to $100 for most shipments
- Perfect for time-sensitive items like critical documents or perishable goods
Priority Mail Express comes with a money-back guarantee if USPS doesn’t meet their published delivery window.
USPS Ground Advantage
- Cost-effective option for larger or heavier packages that don’t require Priority Mail’s speed
- Previously known, in part, as Retail Ground or Parcel Select Ground
- Takes up to 2–5 business days or longer, depending on distance
- Weight limit: 70 lbs, with possible dimensional weight surcharges for larger boxes
Ground Advantage is often chosen when budget is a bigger priority than speed.
USPS Marketing Mail (Commercial)
- Primarily for businesses sending advertisements, catalogs, or newsletters in bulk
- Requires commercial or bulk mailing permits
- Rates and size limits differ from typical package services
- Delivery times vary more widely, often taking 2–9 days
Size Limits by Service
First-Class Package Service Size Limits
- Maximum Weight: 13 oz at retail; up to 15.999 oz for commercial shippers
- Dimensions: Must be at least large enough to contain the shipping label and barcode
- Packages exceeding 108 inches in combined length + girth generally aren’t applicable for First-Class Package since the weight limit is so low
Typical Dimensions:
- Minimum length: 6 inches
- Minimum height: 3 inches
- Maximum length for Large Envelopes/Flats: 15 inches
If your parcel is heavier than 15.999 oz (commercial) or 13 oz (retail), you must move to another USPS service (e.g., Priority Mail).
Priority Mail Size Limits
- Maximum Weight: 70 lbs
- Maximum Combined Length + Girth: 108 inches
- Parcels bigger than 1 cubic foot may be subject to dimensional weight if traveling to certain zones
- For oversized packages (combined length + girth > 108 inches but <= 130 inches), USPS may apply oversize pricing or direct you to Priority Mail or Ground Advantage with applicable surcharges
Priority Mail Express Size Limits
- Maximum Weight: 70 lbs
- Maximum Combined Length + Girth: 108 inches
- Similar DIM weight rules for larger packages
- Packages exceeding 108 inches in length + girth may not qualify for Priority Mail Express
Priority Mail Express shipping boxes and envelopes (Flat Rate) can be used if your items fit, usually ignoring weight-based costs as long as it’s under 70 lbs.
Ground Advantage Size Limits
- Maximum Weight: 70 lbs
- Maximum Combined Length + Girth: 130 inches
- If length + girth exceeds 108 inches, the package is generally considered oversize, which can lead to extra fees
- Also subject to dimensional weight if the package volume is large relative to its weight
Ground Advantage can handle large parcels, but the delivery time is slower compared to Priority Mail.
Dimensional (DIM) Weight Pricing
Dimensional weight comes into play when shipping large, lightweight boxes. Instead of billing purely by the actual weight, USPS calculates an equivalent “dimensional weight” based on the box’s volume. You pay whichever is higher: actual weight or dimensional weight.
To calculate DIM weight (for domestic shipping), USPS uses a standard formula:
DIM Weight (in lbs) = (Length x Width x Height) / 166
- Round up to the next whole number if you get a fraction
- DIM weight pricing primarily affects Priority Mail and Ground Advantage services for bigger packages
Example:
- A box measuring 18″ x 18″ x 18″ has a volume of 5832 cubic inches
- DIM Weight = 5832 ÷ 166 ≈ 35.1 lbs
- If the actual weight is only 20 lbs, you’d be charged for 36 lbs (rounding up from 35.1)
Flat Rate, Regional Rate, and Special USPS Packaging
Flat Rate Boxes and Envelopes
Priority Mail Flat Rate allows you to ship any weight (up to 70 lbs) nationwide at a fixed price as long as it fits in the USPS Flat Rate packaging.
Options include Small, Medium, Large Flat Rate Boxes, and Flat Rate Envelopes.
These are great for heavy items that fit in the provided packaging, especially if shipping to a distant zone.
Regional Rate Boxes
Regional Rate Boxes (Box A and Box B) are specific to Priority Mail, offering a cost advantage for shorter-distance shipments if your items fit.
Price is determined by the box type (A or B) and the destination zone.
Weight limits typically range from 15 to 20 lbs depending on the box type.
Free USPS Packaging
Using USPS-branded boxes and envelopes for Priority Mail, Priority Mail Express, and Flat Rate options can save you money. You can pick them up free of charge at the Post Office or order them online.
Tips for Choosing the Right Package Size and Service
Check Weight First
If you’re under 13 oz (retail) or 15.999 oz (commercial), First-Class Package might be the cheapest option. Otherwise, compare Priority Mail, Ground Advantage, or Priority Mail Express based on speed and budget.
Measure Carefully
Always confirm both length and girth. Large, lightweight parcels may incur DIM weight charges. Overestimating or underestimating size could result in unexpected fees or delivery delays.
Use Flat Rate When Heavier
If your package is heavy but fits in a Flat Rate box/envelope, it could be cheaper than paying based on weight and zone.
Consider Speed vs. Cost
Priority Mail is typically 1–3 days; Ground Advantage can be slower but cheaper. If you’re not in a hurry, Ground Advantage might save you money. If you’re shipping time-sensitive or valuable items, Priority Mail or Priority Mail Express is worth the extra cost.
Compare Regional Rate Boxes
If shipping to nearby zones, Regional Rate could be more economical than Flat Rate—especially if your item is relatively heavy but fits within the box’s weight limit.
Keep Dimensional Weight in Mind
For larger boxes, double-check if DIM weight pricing applies. You might reduce shipping costs by using more compact packaging or by using Flat/Regional Rate options.
Take Advantage of Free Supplies
USPS provides free packaging for Priority Mail, Priority Mail Express, and Flat Rate shipments. Order supplies online or pick them up at the Post Office.
Frequently Asked Questions (FAQs)
What happens if my package is bigger than the USPS size limits?
USPS may refuse your package or require you to use a different service (e.g., freight shipping). You may also face significant oversize surcharges.
Do I pay extra if my package exceeds 108 inches in length + girth?
If you’re using Priority Mail or Ground Advantage, packages over 108 inches (but under 130 inches) are generally considered “oversized” and can incur additional handling fees.
Can I use my own box for Priority Mail Flat Rate?
No, Flat Rate pricing only applies to official USPS Flat Rate-labeled boxes and envelopes. If you use your own packaging, normal Priority Mail rates apply (weight- and zone-based).
Is there a maximum length for First-Class Packages?
First-Class Package Service is designed for small parcels (up to 13 oz retail/15.999 oz commercial). While there’s no explicit large dimension threshold like Priority Mail, the service is practically limited by weight and standard letter/package dimensions.
Is there a surcharge for irregularly shaped packages?
Yes, certain non-rectangular items (tubes, triangular boxes) or extremely large packages might incur non-machinable or oversize surcharges. Check USPS guidelines for specifics.
How does USPS measure length and girth in-store?
A USPS clerk typically places the package on a scale, measures the longest dimension (length), and then measures around the thickest part of the box (girth) with a measuring tape. They’ll confirm the combined length + girth and check weight or dimensional weight if applicable.
Can I ship large, lightweight items without paying DIM weight charges?
If your package meets certain dimensional thresholds, DIM weight pricing will apply for Priority Mail or Ground Advantage. To avoid extra fees, consider Flat Rate (if it fits) or reconfigure your packaging.
Calculate length and girth carefully to avoid surprises. For small, lightweight parcels, First-Class Package often offers the best value. Priority Mail is a great choice for shipments up to 70 lbs needing faster delivery. Priority Mail Express is ideal for urgent, time-sensitive shipments. Ground Advantage is a budget-friendly option for non-urgent, heavier or larger items.
Dimensional weight can increase costs if you ship large but lightweight packages, so consider Flat Rate or more compact packaging. Free USPS supplies are available for Priority Mail, Priority Mail Express, and Flat Rate services.
By pairing the correct service with the right package size, you’ll save money, reduce transit times where needed, and ensure a smooth shipping experience.
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