How do I find the maximum box size for a DIM weight?

Multiply the target weight by the divisor for the maximum volume, then divide by the two sides you know to get the largest third side.

What is the largest box for 20 lb at a 139 divisor?

Any box up to 2,780 in³. With a 16 × 12 in base, the height can be about 14.479 in, or 14 in in whole inches.

Why should I round the third side down?

Rounding up would push the volume — and the dimensional weight — over the limit.

What if the two fixed sides are already too big?

Then no useful third side keeps the box within the target. Choose a smaller footprint or a higher target.

Does this work in centimeters?

Yes. At 10 kg and 5,000 cm³/kg the limit is 50,000 cm³; on a 40 × 30 cm base that is about 41.66 cm of height.

Illustration of a box footprint with its height growing up to a dashed maximum line

Shipping & packaging

How to Find the Largest Box Under a DIM Weight Limit

If you want a package to stay at or under a certain dimensional weight, you can work backwards from the weight to a volume, and from the volume to the one side you haven’t decided yet. The only care needed is with rounding: a box that is exactly on the limit can round up past it.

Ready to try the tool this guide describes?

Open Maximum Box Size for Target DIM Weight Calculator →

Step 1: turn the weight into a volume

Maximum volume = target weight × divisor. At 20 lb and a 139 divisor, the box can be up to 2,780 in³. At 10 kg and 5,000 cm³/kg, up to 50,000 cm³.

Step 2: divide by the sides you know

With two sides fixed, the third is the volume divided by their product. A 16 × 12 in footprint is 192 in², so the height can be up to 2,780 ÷ 192 = 14.479 in. An 18 × 12 in footprint allows 12.87 in.

Step 2: divide by the sides you know comparison
Target and divisor	Fixed sides	Largest third side	Whole units
20 lb, 139 in³/lb	16 × 12 in	14.479 in	14 in
20 lb, 139 in³/lb	18 × 12 in	12.87 in	12 in
10 kg, 5,000 cm³/kg	40 × 30 cm	41.66 cm	41 cm

Step 3: round down and check

Always round the third side down. Then work the dimensional weight forward again: 16 × 12 × 14 in is 2,688 in³, or 19.34 lb, which rounds up to 20 lb — within the target. 18 × 12 × 12 in is 18.65 lb, billed as 19 lb.

If your carrier rounds dimensions up, round the fixed sides up first, then find the third.

When the weight rounding matters

With weights rounded up to whole pounds, a target of 20.6 lb behaves like 20 lb: anything over 20 lb bills as 21. Use the highest whole (or half) unit at or under your target as the real limit.

Quick method

Multiply the target by the divisor.
Divide by the two fixed sides.
Round the result down to a size you can buy or make.
Recalculate the dimensional weight to confirm it stays within the target.

Largest Box Under a DIM Limit FAQ

How do I find the maximum box size for a DIM weight?: Multiply the target weight by the divisor for the maximum volume, then divide by the two sides you know to get the largest third side.
What is the largest box for 20 lb at a 139 divisor?: Any box up to 2,780 in³. With a 16 × 12 in base, the height can be about 14.479 in, or 14 in in whole inches.
Why should I round the third side down?: Rounding up would push the volume — and the dimensional weight — over the limit.
What if the two fixed sides are already too big?: Then no useful third side keeps the box within the target. Choose a smaller footprint or a higher target.
Does this work in centimeters?: Yes. At 10 kg and 5,000 cm³/kg the limit is 50,000 cm³; on a 40 × 30 cm base that is about 41.66 cm of height.