Calculate package girth and length plus girth from box or tube dimensions in inches or cm, and compare the total with USPS and UPS size limits.
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Girth Formula
The calculator uses the two smallest dimensions of an object to calculate girth. This is common for shipping and package measurement, where girth means the distance around the thickest part of a rectangular package, excluding the longest side.
To solve for the smallest dimension:
To solve for the second smallest dimension:
- G = girth
- S = smallest dimension
- T = second smallest dimension
The three rectangular-girth modes let you enter two values and solve for girth, the smallest dimension, or the second-smallest dimension. The separate box and tube modes calculate length plus girth; maximum-length mode reverse-solves a feasible axial length under the selected unrounded carrier thresholds. UPS tube comparison uses the enclosing-box perimeter, 4 times diameter; USPS tube girth uses the circular circumference, pi times diameter.
Each input is converted independently to inches before the formula is applied. The result is converted to the selected result unit. These are unrounded geometric calculations, not carrier-rounded acceptance or pricing measurements.
Length Unit Conversions Used for Girth
These are the conversion factors used to place all measurements into the same base unit before calculation.
| Unit | Millimeter Equivalent | Common Use |
|---|---|---|
| mm | 1 mm | Small precise measurements |
| cm | 10 mm | Small packages and objects |
| m | 1000 mm | Large objects |
| in | 25.4 mm | Shipping dimensions in inches |
| ft | 304.8 mm | Large package dimensions |
| yd | 914.4 mm | Oversized measurements |
Common Girth Calculations for Rectangular Packages
| Smallest Dimension | Second Smallest Dimension | Girth |
|---|---|---|
| 4 in | 6 in | 20 in |
| 8 in | 10 in | 36 in |
| 12 in | 18 in | 60 in |
| 20 cm | 30 cm | 100 cm |
Example Girth Calculations
Example 1: Calculate girth
You have a package with a smallest dimension of 8 inches and a second smallest dimension of 10 inches.
The girth is 36 inches.
Example 2: Calculate the missing smallest dimension
You know the girth is 60 centimeters and the second smallest dimension is 20 centimeters.
The smallest dimension is 10 centimeters.
FAQ
What does girth mean for a package?
For a rectangular package, girth is the distance around the package using the two smaller dimensions. It is calculated as twice the sum of the smallest dimension and the second smallest dimension.
Do I include the longest side when calculating girth?
No. Girth itself uses the two dimensions perpendicular to the longest side. The box and tube length-plus-girth modes add the longest dimension separately. Carrier comparison and maximum-length results do not establish shipping eligibility.
Can the dimensions use different units?
Yes. Each dimension can use mm, cm, m, in, ft or yd independently. The calculator normalizes the inputs to inches, applies the selected formula, and converts the answer into the selected result unit.
