acalculator

What is the dimensional weight?

Enter the box’s length, width and height and the carrier’s divisor. The dimensional weight calculator shows the DIM weight, rounded up, and the billable weight once you add the actual weight.

Your numbers

Units
Divisor units
Round each side
139 at many US carriers’ daily rates; 166 at USPS and some retail rates.
Billable weight
13 lb

The billable weight is 13 lb; the dimensional weight is 12.43.

Dimensional weight (lb or kg)
12.43
Dimensional weight, rounded up
13
Billable weight (lb or kg)
13
Volume (in³ or cm³)
1,728

Billable weight: 13 lb. The billable weight is 13 lb; the dimensional weight is 12.43.

How to calculate

Works out a package’s dimensional (volumetric) weight from its length, width and height and the carrier’s divisor, and the billable weight: the larger of the dimensional and actual weights.

Example with the default inputs (Divisor units in and lb, Length 12 in, Width 12 in, Height 12 in, Round each side Nearest whole, Divisor (in³ per lb) 139): The billable weight is 13 lb; the dimensional weight is 12.43.

Method: Dimensional weight = L × W × H ÷ divisor (in³ per lb, or cm³ per kg), each side first rounded as chosen; rounded up to the next whole lb or kg. Billable weight = the larger of that and the actual weight rounded up.

  • Carriers set their own divisors and rounding rules, and change them. Check the carrier’s current rules for your account.
  • Some services charge dimensional weight only above a size (USPS: over 1 cubic foot, 1,728 in³). The page always shows it.
  • The steps are exact on the numbers as typed; only the final roundings are shown.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Divisor units in and lb, Length 12 in, Width 12 in, Height 12 in, Round each side Nearest whole, Divisor (in³ per lb) 139 gives Dimensional weight (lb or kg) 12.431655, Dimensional weight, rounded up 13, Billable weight (lb or kg) 13, Volume (in³ or cm³) 1,728, Billable weight 13 lb.Source: FedEx, "What is dimensional weight?" (L × W × H in inches, each rounded to the nearest whole inch, ÷ 139), https://www.fedex.com/en-us/shipping/packaging/what-is-dimensional-weight.html (retrieved 2026-10-05)
  2. Divisor units in and lb, Length 12 in, Width 12 in, Height 12 in, Round each side Nearest whole, Divisor (in³ per lb) 166, Actual weight 5 lb gives Dimensional weight (lb or kg) 10.409639, Dimensional weight, rounded up 11, Billable weight (lb or kg) 11, Billable weight 11 lb, by size.Source: USPS Postal Bulletin 22509 (round each measurement to the nearest whole inch, divide by 166 and round up to the next whole pound), https://about.usps.com/postal-bulletin/2018/pb22509/html/updt_002.htm (retrieved 2026-10-05)
  3. Divisor units cm and kg, Length 14.17 in, Width 9.843 in, Height 6.299 in, Round each side Nearest whole, Divisor (cm³ per kg) 5,000 gives Dimensional weight (lb or kg) 2.88, Dimensional weight, rounded up 3, Volume (in³ or cm³) 14,400.Source: FedEx UK, "Understand dimensional weight" (36 × 25 × 16 cm ÷ 5,000 is a DIM weight of 3 kg), https://www.fedex.com/en-gb/how-to/calculate-costs/dimensional-weight.html (retrieved 2026-10-05)
  4. Divisor units in and lb, Length 12.4 in, Width 10.6 in, Height 8.5 in, Round each side Up, Divisor (in³ per lb) 139, Actual weight 14 lb gives Volume (in³ or cm³) 1,287, Dimensional weight (lb or kg) 9.258993, Dimensional weight, rounded up 10, Billable weight (lb or kg) 14, Billable weight 14 lb, by weight.Source: FedEx, "What is dimensional weight?" (L × W × H in inches, each rounded to the nearest whole inch, ÷ 139), https://www.fedex.com/en-us/shipping/packaging/what-is-dimensional-weight.html (retrieved 2026-10-05)
  5. Divisor units in and lb, Length 12.4 in, Width 10.6 in, Height 8.5 in, Round each side Nearest whole, Divisor (in³ per lb) 139 gives Volume (in³ or cm³) 1,188, Dimensional weight, rounded up 9.Source: USPS Postal Bulletin 22509 (round each measurement to the nearest whole inch, divide by 166 and round up to the next whole pound), https://about.usps.com/postal-bulletin/2018/pb22509/html/updt_002.htm (retrieved 2026-10-05) (nearest whole inch)

How it works

  1. Pick the divisor units: inches and pounds, or centimetres and kilograms. The sides are turned into that length unit.
  2. Round each side as chosen: to the nearest whole inch or centimetre (halves up), up to the next whole one, or not at all.
  3. Volume = length × width × height.
  4. Dimensional weight = volume ÷ divisor (cubic inches per pound, or cubic centimetres per kilogram).
  5. Round the dimensional weight up to the next whole pound or kilogram.
  6. If you give the actual weight, round it up to the next whole pound or kilogram too. The billable weight is the larger of the two. The page says "by size" when the dimensional weight wins and "by weight" when the actual weight wins. When the two are equal, or when you give no actual weight, it adds no note.

Rules

  • Every side must round to at least 1 inch or centimetre; a side that rounds to 0 gives no answer.
  • Divisors: 1 to 10,000 in³ per lb, or 100 to 100,000 cm³ per kg.
  • The steps are exact on the numbers as typed; the dimensional weight is shown to 2 decimals and the volume to 10 significant figures.

Worked examples by hand

A 12-inch cube, divisor 139. 12 × 12 × 12 = 1,728 in³. 1,728 ÷ 139 = 12.4317 lb, rounded up to 13 lb.

The same box at divisor 166, weighing 5 lb. 1,728 ÷ 166 = 10.4096, rounded up to 11 lb. 11 lb is more than 5 lb, so the billable weight is 11 lb, by size.

36 × 25 × 16 cm, divisor 5,000. 36 × 25 × 16 = 14,400 cm³. 14,400 ÷ 5,000 = 2.88 kg, rounded up to 3 kg.

12.4 × 10.6 × 8.5 in, sides rounded up, divisor 139, 14 lb. Sides 13 × 11 × 9 = 1,287 in³. 1,287 ÷ 139 = 9.2590, rounded up to 10 lb. The actual 14 lb is more, so the billable weight is 14 lb, by weight.

The same box, sides to the nearest inch. 12.4 → 12, 10.6 → 11, 8.5 → 9 (a half rounds up). 12 × 11 × 9 = 1,188 in³; 1,188 ÷ 139 = 8.5468, rounded up to 9 lb.

Other questions people ask

How do I calculate dimensional weight?

Round each side of the box as the carrier says (often to the nearest whole inch), multiply length × width × height, and divide by the carrier’s divisor. Round the result up to the next whole pound. A 12-inch cube is 1,728 cubic inches; at a divisor of 139 that is 12.43, so 13 lb.

What is the billable weight?

It is the weight the carrier charges for: the larger of the dimensional weight and the actual weight on a scale, each rounded up to the next whole pound or kilogram. A light but bulky box is billed by its size; a small heavy one by its weight.

What divisor should I use?

Use the one your carrier and rate type state. In the US, many carriers use 139 cubic inches per pound for daily rates and 166 for retail rates; USPS uses 166. In centimetres and kilograms, 5,000 cm³ per kg is the most common. A larger divisor gives a lower dimensional weight.

Should I round the sides up or to the nearest inch?

It depends on the carrier and changes over time. FedEx’s and USPS’s published rules round each side to the nearest whole inch; some carriers now round up to the next whole inch. Pick the rule your carrier uses in the "Round each side" box.

Does USPS charge dimensional weight on every package?

No. USPS applies it to packages over one cubic foot (1,728 cubic inches) for the services that use it. The calculator always shows the dimensional weight, so check whether your service applies it.

How can I lower my dimensional weight?

Use the smallest box that fits the item safely. Every inch counts three ways, because the volume multiplies all three sides; cutting a 12-inch cube to 11 inches cuts the volume by almost a quarter.