Frequently
asked.

They're the same shape. "Box" is the everyday word, "cuboid" is the geometry term for a solid with six rectangular faces, and "rectangular prism" describes the same shape by its cross-section. All three are calculated identically: length × width × height.

V = l × w × h. Multiply the three sides. The only rule is that all three must be in the same unit before you multiply — this calculator handles that automatically when you mix units.

Because you've multiplied three lengths together. One length × one length gives an area (square units). One length × one area gives a volume (cubic units). So if you measure in centimeters, the result is cm³ ("cubic centimeters").

One liter equals 1,000 cubic centimeters (or 0.001 cubic meters). Measure in centimeters, multiply length × width × height, then divide by 1,000. The calculator shows both at once.

Divide by 1,728. (Because 1 foot = 12 inches, and 12³ = 1,728.) So a 2,160 in³ package equals 1.25 ft³.

Yes — this is one of the few calculators that supports it. You can enter "2 ft × 50 cm × 18 in" without converting first. The calculator converts each dimension to meters internally and gives you the volume in every common unit.

Yes. The calculator accepts decimals (2.5), simple fractions (1/2), and mixed numbers (2 1/2). Useful when reading a US tape measure.

Dimensional weight (also called volumetric or DIM weight) is a billing weight calculated from a package's volume. Low-density packages — like a big box of pillows — take up a lot of space but weigh very little. Carriers charge whichever is greater: actual weight or dimensional weight. The formula is (L × W × H) ÷ divisor, where the divisor depends on the carrier. See the shipping calculator for live computation.

For US domestic shipments, FedEx and UPS use a divisor of 139 in³/lb. For international shipments, they use 5,000 cm³/kg. USPS Priority Mail uses 166 in³/lb and only applies dim weight to packages over 1 cubic foot. These numbers change occasionally — always verify with the carrier's current tariff.

Girth is the distance around the box, measured perpendicular to the longest side. Formula: 2 × (width + height). UPS and FedEx use "length + girth" to identify oversized packages — anything over 165 cm (65 in) gets handling fees, and the absolute cap is around 330 cm (130 in).

The space diagonal — the longest straight line that fits inside the box — equals √(l² + w² + h²). It's an extension of the Pythagorean theorem to three dimensions. Useful when checking whether a long item will fit inside a box.

Surface area measures the total area of all six faces of the box (in square units), useful for calculating how much wrapping paper or paint you need. Volume measures the enclosed space (in cubic units), useful for capacity or shipping cost.

If the shape is approximately a cuboid (tapered sides count if they're slight), use the average length, width, and height. For truly irregular shapes, break the object into smaller rectangular sections, calculate each, and sum the results — that's what our batch calculator is for.

It depends what you need. For shipping calculations and dimensional weight, carriers always use the outside dimensions. For capacity (how much can fit inside), use the inside dimensions — for thick-walled boxes, the difference can be a few centimeters.