Dimensional weight calculator
Carriers bill on the greater of what your package weighs and what its size says it should weigh. Enter your box and its actual weight to see which one you will be charged for, the divisor used, and where that rule comes from.
Rule status: 0 of 16 carrier rules
in this build have been verified against their official source. The rest come from our
2026-08-30 snapshot. Every result tells you which it used, and links to the
source.
How dimensional weight works
- Multiply length × width × height to get the volume in cubic inches. Some carriers round each dimension up to a whole inch first.
- Divide that volume by the carrier's divisor. A smaller divisor means a higher dimensional weight.
- Round the result the way that carrier rounds it — usually up to the next whole pound.
- Compare it against the package's actual weight. You are billed on the greater of the two, which is called the billable weight.
Some services only apply dimensional weight above a threshold volume. USPS, for instance, applies it above one cubic foot, so a small heavy parcel is billed on its actual weight.
Worked example
A 20 × 14 × 12 in box weighing 5 lb, shipped USPS.
- Volume is 20 × 14 × 12 = 3,360 cu in.
- That is above the 1,728 cu in threshold, so dimensional weight applies.
- 3,360 ÷ 139 = 24.17 lb before rounding.
- Rounded up to the next whole pound, that is 25 lb.
- 25 lb beats the 5 lb the box actually weighs, so the billable weight is 25 lb. You pay for the air.
Edge cases worth knowing
- The divisor is not universal. UPS publishes different divisors for Daily and Retail rates. Using the wrong one changes the answer by roughly 20%.
- Rounding is a carrier rule, not a convention. Where we do not have a carrier's rounding rule on record, we show the unrounded number and say so rather than picking one.
- Measure the outside of the package. Dimensional weight uses the box's outside measurements, including any bulge. This is the opposite of the box-fit tool, which needs inside measurements.
- We do not quote prices. Billable weight is one input to a rate. Zone, service, and surcharges all matter, and we do not have a rating integration.
- Actual weight may be rounded too. Carriers often round the scale weight up before comparing. We compare what you entered.
Common questions
- What is a dimensional weight divisor?
- A number the carrier publishes that converts volume into a weight. A divisor of 139 means every 139 cubic inches counts as one pound.
- Why is my small heavy box not affected?
- Some services only apply dimensional weight above a threshold volume, and a dense package's actual weight usually wins anyway. The calculator says which applied.
- Why will this not give me a FedEx number?
- Because we do not have a verified FedEx divisor on file. FedEx divisors vary by service, and a confident-looking number built on an unconfirmed one is worse than telling you we do not know.
- How do I lower my dimensional weight?
- Use a smaller box. Dimensional weight is a function of volume alone, so packing the same items into less space is the only lever. Check the box fit calculator to see whether a smaller box works.
- Is this the price I will pay?
- No. This is the weight you will be billed on, which is one input to a rate. We do not quote postage.