Dimensions Converter

About this converter

A dimensions converter takes three numbers — length, width, and height — and computes every measurement that follows from them. Each side in millimetres, centimetres, metres, inches, and feet. The floor area. The total surface area of all six faces. The interior volume in cubic metres, cubic feet, US gallons, and litres. The base perimeter. One short calculation gives you the half-dozen numbers you need to order materials, plan a move, fit furniture, or compare two boxes.

The converter is built for everyday cases: storage boxes, packages, room dimensions, fish tanks, ductwork, planter boxes, freight pallets. For curved or irregular shapes — cylinders, cones, L-shaped rooms — see the cylinder calculator, the floor area calculator (which sums multiple rectangles), or the architecture geometry tools, all on the architecture section of this site.

Every input parses both metric and imperial. Type 2.5 m and the converter shows you 98.4 inches. Type 8 ft and you also get 2.44 m, 96 in, and 2,438 mm. The math is exact: there is no rounding in the conversion itself, only in how many decimal places make sense for display.

The math: length → area → volume

The conversions are linear for length, square for area, and cubic for volume. The same factor between metric and imperial appears in each form, just at a different power.

Length: 1 inch = 25.4 mm = 2.54 cm = 0.0254 m. 1 foot = 12 inches = 0.3048 m. These are exact by international agreement; everything else follows from them.

Area: because area is a length squared, the conversion factor squares too. 1 square inch = 25.4² = 645.16 mm². 1 square foot = 0.3048² = 0.0929 m². So an 8-by-6-foot room is 48 ft² = 4.46 m² of floor.

Volume: cubed. 1 cubic inch = 25.4³ = 16,387 mm³. 1 cubic foot = 0.3048³ = 0.02832 m³ = 28.317 L = 7.481 US gallons. So a 2-by-2-by-3-foot cooler is 12 ft³ = 339.6 L = 89.8 US gallons of capacity (which would let you put a small bath's worth of ice and a lot of beer in it).

Worked example. A box 30 inches by 24 inches by 18 inches. Each side: 30 in = 762 mm = 76.2 cm; 24 in = 609.6 mm; 18 in = 457.2 mm. Floor area: 30 × 24 = 720 in² = 0.464 m². Surface area: 2 × (30×24 + 30×18 + 24×18) = 2 × (720 + 540 + 432) = 3,384 in² = 2.18 m². Volume: 30 × 24 × 18 = 12,960 in³ = 7.5 ft³ = 56.1 US gallons.

Imperial vs metric, rounding, and which axis is which

Watch the units. Mixing systems in one calculation is the most common cause of errors. If you have a 6-foot length but a 2-metre width, convert one before multiplying. The converter does this automatically — set the input unit and every output is consistent — but if you do the math by hand, the order matters.

Which axis is which? For boxes and rooms, length is the longest horizontal dimension, width is the shorter horizontal dimension, and height is vertical. For furniture and appliances, the convention is sometimes width-first (the side you face), then depth, then height. The arithmetic does not care; the labels are for your benefit. If you are reading shipping dimensions on a courier's website, they normally write L × W × H in that order.

Floor area versus surface area. Floor area is L × W and tells you how much paint or flooring covers the floor. Surface area is the sum of all six faces and tells you how much paint covers the whole box, the whole room (minus floor), or the whole shipping carton. Don't use floor area when you mean surface area — for paint estimation, you want the wall area, which is 2(L × H) + 2(W × H), and the ceiling area, which is L × W.

Capacity vs volume. The cubic capacity of a container is its internal volume, not its overall size. A box with 1/4-inch wall thickness has slightly less internal volume than its external dimensions suggest; for thin-walled containers (cardboard, plastic), the difference is negligible, but for thick-walled (concrete planters, insulated coolers), measure the inside.