How to Calculate Dimensional Weight (DIM Weight)

You weigh a parcel at 2 lb, buy the label, and the carrier bills you for 15 lb. Nothing went wrong: you just met dimensional weight, often shortened to DIM weight and also called volumetric weight.

This guide shows how to calculate it, which numbers the main carriers use, and how to keep it from eating your margin.

What is dimensional weight?

A truck or a plane fills up by volume long before it fills up by weight. A box of pillows takes the space of a box of books but weighs a fraction of it. To charge fairly for the space, carriers convert the size of a parcel into a “weight”, then compare it with the real weight.

You are billed for whichever is higher. That number is called the billable weight (or chargeable weight).

Term	Meaning
Actual weight	What the parcel weighs on a scale
Dimensional weight	A weight calculated from the parcel’s size
Billable weight	The higher of the two: this is what you pay for

The dimensional weight formula

Dimensional weight = length × width × height ÷ DIM divisor

Measure the outside of the packed box at its longest points, including any bulge.
In inches and pounds, the most common divisor is 139.
In centimetres and kilograms, the most common divisor is 5000.

The divisor (also called the DIM factor) is set by each carrier. A lower divisor means a higher dimensional weight, so it is worse for you.

How to calculate it, step by step

Measure length, width and height of the packed box.
Round each measurement to the nearest whole inch or centimetre. Most carriers round halves up.
Multiply the three numbers to get the volume.
Divide by the carrier’s divisor.
Round the result up to the next whole pound (or the next half kilogram, depending on the carrier).
Compare with the actual weight. The higher number is your billable weight.

Example in inches

A box measures 18 × 14 × 10 inches and weighs 6 lb.

Volume: 18 × 14 × 10 = 2,520 cubic inches
Dimensional weight: 2,520 ÷ 139 = 18.1, rounded up to 19 lb
Actual weight: 6 lb
Billable weight: 19 lb

You pay for more than three times the real weight.

Example in centimetres

A box measures 40 × 30 × 20 cm and weighs 3 kg.

Volume: 40 × 30 × 20 = 24,000 cubic centimetres
Dimensional weight: 24,000 ÷ 5000 = 4.8 kg
Actual weight: 3 kg
Billable weight: 4.8 kg before rounding (most carriers would bill 5 kg)

When the real weight wins

A box of 10 × 8 × 6 inches weighs 9 lb. Its dimensional weight is 480 ÷ 139 = 3.5, rounded up to 4 lb. The actual weight is higher, so you simply pay for 9 lb. Small, dense products are rarely affected.

DIM divisors by carrier

These are the commonly published divisors at the time of writing. Carriers change their rules, and negotiated accounts can have different divisors, so always check the carrier’s current service guide.

Carrier	Inches and pounds	Centimetres and kilograms	Good to know
UPS	139	5000	Applies to all parcels on standard (daily) rates
FedEx	139	5000	Applies to all parcels
DHL Express	139	5000	Applies to all parcels
USPS	166	Not applicable	Only for parcels larger than 1 cubic foot (1,728 cubic inches)

The USPS rule matters for small sellers in the United States. A parcel under one cubic foot is charged on its actual weight, which is why light, medium-sized parcels are often cheaper with USPS.

Same box, different carrier: take the 18 × 14 × 10 inch box from above. With a divisor of 139 it is billed at 19 lb. With the USPS divisor of 166 it comes to 2,520 ÷ 166 = 15.2, billed at 16 lb.

A formula for your spreadsheet

If your box dimensions are in cells A2, B2 and C2 and the actual weight is in D2:

Dimensional weight: =ROUNDUP(A2*B2*C2/139, 0)
Billable weight: =MAX(D2, ROUNDUP(A2*B2*C2/139, 0))

Change 139 to the divisor of the carrier you use. Do this once for each of your standard box sizes and you will know your billable weight before you ever buy a label.

How to lower your dimensional weight

Use the smallest box that protects the product. Cutting two inches from each side of an 18 × 14 × 10 box drops its dimensional weight from 19 lb to 12 lb.
Switch soft goods to poly mailers. Clothing and textiles do not need a box.
Keep three or four box sizes matched to your best-sellers instead of one big box for everything.
Compress what can be compressed. Vacuum bags work well for cushions, bedding and plush items.
Compare carriers per box size. The carrier with the best price for a small heavy box is often not the best for a large light one.
Measure accurately. If the carrier re-measures your parcel and finds it bigger, you pay the difference plus, sometimes, a correction fee.

More ideas are in our guide on how to reduce shipping costs, and the options by parcel type are in the cheapest way to ship packages.

Common questions

Is dimensional weight the same as volumetric weight?

Yes. “Dimensional weight”, “DIM weight” and “volumetric weight” describe the same idea. “Volumetric” is more common outside North America.

Does dimensional weight apply to every parcel?

With UPS, FedEx and DHL Express, yes: every parcel is checked. With USPS it only applies above one cubic foot. Flat-rate services are the exception everywhere: the price depends on the box, not the weight.

What is a cubic foot in practice?

1,728 cubic inches, which is a 12 × 12 × 12 inch box. A 14 × 12 × 10 inch box (1,680 cubic inches) stays just under it.

Key takeaways

Dimensional weight = length × width × height ÷ divisor. You pay for the higher of dimensional and actual weight.
The usual divisors are 139 (inches and pounds) and 5000 (centimetres and kilograms). USPS uses 166, and only above one cubic foot.
Smaller packaging is the most reliable way to pay less.
Put the formula in a spreadsheet once for your standard boxes so there are no surprises on the invoice.