Steel Weight Calculator

Background.

Steel is heavy in a way that catches people out. A single plate two metres by one and a half and only ten millimetres thick weighs 235.5 kg, roughly what three adults weigh together. That figure decides whether a delivery needs a crane or a forklift, whether a mezzanine can take a stack of offcuts, and what a stockholder charges, because steel is bought and priced by weight.

The arithmetic is short because one number, the density, barely changes from one carbon-steel job to the next. Plain carbon steel is close to 7,850 kg per cubic metre, the value filled in here; Eurocode 3 uses exactly that figure for structural steel, and American structural practice uses 490 lb per cubic foot, which is within a kilogram per cubic metre of it. Multiply the volume of a piece by that density and you have its mass. A handy consequence: each millimetre of plate thickness adds 7.85 kg to every square metre, so 6 mm plate comes to 47.1 kg/m² and 20 mm plate to 157 kg/m².

The shape assumed is a solid rectangular block, length times width times thickness, repeated for however many identical pieces you enter. That suits plate, sheet, flat bar and square bar. It does not suit round bar, tube, angle, channel or I-beams, whose cross-sections are not rectangles; for those use the section's published weight per metre or a calculator built for that profile.

The density box is editable on purpose. Austenitic stainless grades such as 304 run slightly heavier, about 7,900 to 8,000 kg/m³, and you can type in another metal entirely, such as aluminium at roughly 2,700. What no density can capture is holes, cut-outs, chamfers, galvanising or the tolerance a mill allows on thickness, so a real piece will come out a little lighter or heavier than the figure here.

What is steel weight calculator?

Steel weight, as used on delivery notes and price lists, is the mass of the steel: its volume multiplied by its density. Here the volume is that of one or more solid rectangular pieces in cubic metres, the density is in kilograms per cubic metre, and the result is given in kilograms and pounds. Physicists would call the force of gravity on that mass the weight, but in the workshop and the steel trade the two words mean the same thing. The trade uses two versions of it. Theoretical weight is the figure calculated from nominal dimensions and a standard density, exactly as done here, and it is what most price lists and cutting schedules quote. Actual weight is what a weighbridge or crane scale records, and it differs from the theoretical figure by the rolling tolerance on thickness, any coating, and whatever holes and cut-outs the fabricator has made. Long products are usually listed in kilograms per metre and plate in kilograms per square metre, so it helps to know how to get both from the calculation.

How to use this calculator.

1. 01Enter length, width and thickness in metres, not millimetres. A 10 mm plate is 0.01 and a 3/8-inch plate is 0.009525; typing 10 for a 10 mm thickness makes the answer a thousand times too large.
2. 02Leave the steel density at 7,850 kg/m³ for mild or structural carbon steel. Change it only if a mill certificate or supplier datasheet gives a different value, such as about 8,000 for 304 stainless.
3. 03Set the number of pieces to the count of identical items. If your cutting list has several sizes, run each size on its own and add the totals.
4. 04For beams and channels, skip the calculation: the section's designation usually carries its weight per unit length, as one of the questions below shows. Angles are named by leg size and thickness instead, so take their weight per metre from the supplier's table.
5. 05Read the total mass in kilograms, use the pound figure for imperial quotes or lifting gear rated in pounds, and glance at the total volume as a check that the dimensions went in as intended.

The formula.

Mass = length × width × thickness × quantity × density. Length, width and thickness, all in metres, give the volume of one piece in cubic metres; multiplying by the number of pieces gives the total volume reported with the result. Density in kilograms per cubic metre turns that volume into kilograms. The pound figure is the kilogram total multiplied by 2.2046226218, which is 1 ÷ 0.45359237, the exact number of kilograms that defines one pound. Every term is a plain multiplier, so the answer is directly proportional to each: double the thickness and the mass doubles. Density moves least of all, about 2% between carbon steel and common stainless grades, so in practice the dimensions, and above all getting thickness into metres, decide whether the answer is right. In imperial terms 7,850 kg/m³ is about 490 lb per cubic foot, or 40.8 lb per square foot for each inch of plate thickness.

The model makes three assumptions worth knowing. Each piece is a solid rectangular block, so the volume is exact for plate, sheet and flat or square bar and wrong for anything with a curved or hollow cross-section unless you adapt it, as several questions below show. The density is uniform, which is true to a fraction of a per cent for rolled steel. And the pieces are identical, so the quantity scales the result in a straight line. Because thickness is a straight multiplier too, small deviations in it pass straight through: a nominal 10 mm plate that actually measures 10.3 mm weighs 3% more than its theoretical figure. To turn the mass into a force, as an engineer checking a floor or a lifting point would, multiply by 9.81 m/s²: the 706.5 kg of the worked example presses down with about 6.93 kN.

A worked example.

Frequently asked questions.

References& sources.

1. [1]NIST. Engineering material reference. Steel density reference. Retrieved 2026-08-06.
2. [2]National Institute of Standards and Technology. NIST SI Guide, 2008 edition. Appendix B unit relationships. Retrieved 2026-08-06.
3. [3]International Code Council. 2021 International Residential Code. Building construction context. Retrieved 2026-08-06.
4. [4]U.S. Department of Agriculture Forest Products Laboratory. Wood Handbook 2021. Engineering materials and construction. Retrieved 2026-08-06.
5. [5]Occupational Safety and Health Administration. Construction standards current 2026. 29 CFR Part 1926 construction safety. Retrieved 2026-08-06.