How to Calculate Dimensional Weight
Follow this step-by-step guide to calculate dimensional weight for your shipments. We'll cover the formula, carrier divisors, and provide worked examples you can follow.
Step-by-Step Method
Measure Your Package
Measure the length, width, and height of your package from the outside. Use centimeters for metric or inches for imperial. Round up to the nearest whole unit.
Tip: For irregularly shaped packages, measure the longest point in each direction. Carriers bill based on the maximum dimensions.
Calculate the Volume
Multiply length × width × height to get the volume in cubic centimeters (cm³) or cubic inches (in³).
Choose the Correct Divisor
Select the divisor based on your carrier and service level. Common divisors are:
Metric (cm → kg)
- Express: 5000
- Economy: 6000
Imperial (in → lb)
- Express: 139
- Economy: 166
Divide Volume by Divisor
Divide your calculated volume by the divisor to get the dimensional weight.
Compare with Actual Weight
Weigh your package on a scale. Compare actual weight to dimensional weight. The higher value is your chargeable weight.
Chargeable Weight = MAX(Actual Weight, Dimensional Weight)
Worked Example
Calculating dimensional weight for a FedEx Express shipment
Length:
60 cm
Width:
40 cm
Height:
35 cm
Actual weight:
10 kg
Divisor (Express):
5000
Calculation:
- Volume = 60 × 40 × 35 = 84,000 cm³
- Dimensional weight = 84,000 ÷ 5000 = 16.8 kg
- Compare: Actual (10 kg) vs Dimensional (16.8 kg)
- Chargeable weight = 16.8 kg
Result: Despite the package weighing only 10 kg, you'll be charged for 16.8 kg. With 0.5 kg rounding, this becomes 17 kg.
Skip the Math
Use our free calculator to get instant dimensional weight results with carrier presets.
Practical Tips
Right-size your packaging
Use the smallest box that safely fits your items. Every extra centimeter increases dimensional weight.
Check carrier-specific rules
Divisors can vary by account, service, and route. Confirm with your carrier for exact figures.
Consider economy services
Economy services often use a higher divisor (6000 vs 5000), resulting in lower dimensional weight charges.
Document your measurements
Take photos of your measurements. This helps resolve disputes if the carrier's measurements differ.
Key Definitions
- Dimensional Weight
- Weight calculated from package dimensions.
- Divisor
- The number used to convert volume to weight.
- Chargeable Weight
- The greater of actual or dimensional weight.
Frequently Asked Questions
What units should I use for dimensional weight?
Use consistent units throughout. For metric, measure in centimeters and use divisor 5000 or 6000 to get kilograms. For imperial, measure in inches and use divisor 139 or 166 to get pounds. Don't mix units.
Why do different carriers use different divisors?
Carriers set divisors based on their cargo capacity, service level, and pricing strategy. Express services with premium pricing use lower divisors (5000), while economy services use higher divisors (6000) that result in lower dimensional weights.
Should I measure the inside or outside of the box?
Always measure the outside dimensions of the box. Carriers measure packages from the outside, including any bulges or irregular shapes. Round up to the nearest centimeter or inch.
How do I calculate dimensional weight for irregular shapes?
Measure the longest point in each direction (length, width, height) to create an imaginary rectangular box around the item. Use these maximum dimensions for your calculation.
Does dimensional weight apply to heavy packages?
Yes, but for dense, heavy packages, actual weight often exceeds dimensional weight. Carriers always use the higher value. Dimensional weight typically matters more for light, bulky items.