# Dimensional weight divisors by carrier

> The divisor, not the tape measure, decides whether a light box is billed as a heavy one.

Live HTML: https://plaintools.io/guides/dimensional-weight-divisors

Updated: 2026-09-07

## What DIM weight is

Couriers convert volume to a billable weight so air and van space is not given away to light, bulky cartons. You pay the greater of the scale weight and the dimensional weight. The conversion is volume divided by a divisor the carrier publishes for that product.

| Product (typical) | Inches divisor | Cm divisor |
| --- | --- | --- |
| FedEx Express/Ground | 139 | 5000 |
| UPS daily / commercial | 139 | 5000 |
| UPS retail / UPS Store | 166 | 6000 |
| USPS Priority (over 1 cu ft) | 166 | 6000 |
| DHL Express | 139 | 5000 |
| IATA air cargo rule of thumb | 166 | 6000 |

## Royal Mail is not in this table

UK consumer Letter and Parcel products use maximum centimetres and grams, not L×W×H/divisor. Do not DIM a Large Letter. Use the parcel size checker for Royal Mail; use the dimensional weight calculator for FedEx, UPS, DHL, and similar.

## How to use the divisor

Measure the boxed outer inches or centimetres. Multiply the three sides. Divide by the preset. Compare to the scale weight. The calculator rounds in the usual billable direction for the unit system you picked.

Contract accounts sometimes get a different divisor than walk-up retail. If your invoice disagrees, the invoice’s divisor is the one that was applied.

## FAQs

### Why is 139 ‘more expensive’ than 166?

A smaller divisor produces a higher DIM weight from the same box, so more shipments hit volumetric billing.

## Related tools

- [Dimensional weight calculator](https://plaintools.io/shipping/dimensional-weight-calculator.md) — HTML: https://plaintools.io/shipping/dimensional-weight-calculator
- [UK parcel size checker](https://plaintools.io/shipping/uk-parcel-size-checker.md) — HTML: https://plaintools.io/shipping/uk-parcel-size-checker

## Related guides

- [Royal Mail Large Letter vs Small Parcel](https://plaintools.io/guides/royal-mail-large-letter-vs-small-parcel.md) — HTML: https://plaintools.io/guides/royal-mail-large-letter-vs-small-parcel