Calculate girth or a missing smallest dimension from any two values with unit support for mm, cm, m, in, ft, and yd, plus step-by-step results.
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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.
G = 2(S + T)
To solve for the smallest dimension:
S = (G / 2) - T
To solve for the second smallest dimension:
T = (G / 2) - S
- G = girth
- S = smallest dimension
- T = second smallest dimension
The calculator lets you enter any two values and solves for the missing one. If you enter the smallest dimension and the second smallest dimension, it calculates girth. If you enter girth and one dimension, it calculates the missing dimension.
All values are converted to millimeters internally before the formula is applied. The result is then converted back to the unit you selected.
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.
G = 2(8 + 10)
G = 36 in
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.
S = (60 / 2) - 20
S = 10 cm
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. This calculator only uses the two smallest dimensions. The longest side is not part of the girth formula. Some shipping rules use length plus girth, but girth itself does not include the longest side.
Can the dimensions use different units?
Yes. You can enter each value in a different supported unit. The calculator converts the values to millimeters, applies the formula, and then converts the answer into the unit selected for the missing field.
