Maximum sizes & weights for USPS services
Domestic services
USPS Ground Advantage
Maximum Size: 130” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
USPS Ground Advantage Cubic
Maximum Size for Boxes: 18" in any single dimension, and total volume cannot exceed 1 cubic feet
Maximum Size for Envelopes: 36” combined Length + Width
Maximum Weight: 20 lbs (320 ounces)
Weight-Based Priority Mail
Maximum Size: 108” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
Priority Mail Cubic
Maximum Size: 18" in any dimension, total volume cannot exceed 0.5 cubic feet
Cubic Softpack Maximum Size: 36” combined Length + Width
Maximum Weight: 20 lbs (320 ounces)
Priority Mail Flat Rate
Maximum Weight: 70 lbs (1120 ounces)
Priority Mail Express
Maximum Size: 108” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
Media Mail
Maximum Size: 108” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
International services
First Class Package International
Maximum Size: 24″ in any dimension, 36″ combined Length + Width + Height
Maximum Weight: 4 lbs (64 ounces)
Simple Export Rate
Maximum Size: 22″ in any dimension, 36″ combined Length + Width + Height
Maximum Weight: 4 lbs (64 ounces)
Priority Mail International
Maximum Size: 108” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
Maximum Length: Varies by country*
Priority Mail International Flat Rate
Maximum Weight for Flat Rate Envelope and Small Flat Rate Box: 4 lbs (64 ounces)
Maximum Weight for Medium and Large Flat Rate Box: 20 lbs (320 ounces)
Priority Mail Express International
Maximum Size: 79” combined Length + Girth
Maximum Weight: 70 lbs (1120 ounces)
Maximum Length: Varies by country*
Size shipping tips
*When shipping internationally, there may be differences in the maximum weight and package dimensions based on what your destination country and USPS have agreed upon.
You can check out specific size and weight limits for each country here: https://pe.usps.com/text/Imm/ab_toc.htm
Look out for Dimensional Weight on your light, oversized packages.
Learn more about Dimensional Weight charges and how to avoid them.
How to calculate the girth of your package
Calculating Girth: To calculate the girth of your package, apply the following steps:
1. Measure the three dimensions of your box, in inches. For example, let's say your box is 10x9x8".
2. Add the measurements of the two smallest dimensions together (in this case, 9" plus 8" equals 17"). Multiply that number by two, and you've got the girth 👍
3. In the example above, the girth of this package is 34".
Pirate Ship rounds dimensions and weight according to USPS practices
Dimensions & Weight Get Rounded Up or Down: When you enter your package's info, Pirate Ship automatically rounds your dimensions and weight to calculate your shipping costs. You should always still enter your package's actual dimensions - we only do this so your package's weights and dimensions are in accordance with USPS rounding practices 😉
Don't Enter the Dimensions Printed on the Box: While you may see dimensions printed on your packaging, we always suggest measuring your packages yourself. These measurements you see can sometimes be your box's inner dimensions, and if you enter them, it may lead to carrier adjustments 🙈
For more info on inner vs. outer dimensions, see our article: Inner Dimensions vs. Outer Dimensions: What's the Difference?
Weights are rounded up to the nearest whole pound
Rounding Weight: USPS rounds your package's weight to the nearest whole pound when calculating shipping costs.
For instance, if you enter your package's weight as 10 lbs, you'll be billed for the 10 lb rate. However, if you enter any value between 10 - 11 lbs (10.3 lbs, for instance), you'll be billed at the 11 lb rate.
Dimensions are rounded up or down to the nearest whole inch
Rounding Dimensions: USPS rounds package dimensions to the nearest whole inch, rounding up or down based on 0.5 inches. If a dimension's decimal value is less than 0.5, that dimension is rounded down. If its decimal value is greater than 0.5, that dimension is rounded up.
For instance, if you enter your package's dimensions as 14.2 x 11.7 x 8.4", our software will automatically round the dimensions to 14 x 12 x 8" 👌