Metal Weight Calculator

Background.

Steel is ordered by length but priced, shipped and lifted by mass, so converting one into the other comes up all the time: a fabricator pricing a job, a site supervisor deciding whether two people can carry an offcut, a buyer comparing a per-kilogram quote with a per-length one. For solid stock the conversion needs only the shape of the cross-section and the density of the metal.

Two shapes are handled. A plate or rectangular bar has a cross-section of width times thickness; a round bar has a circle, π times the radius squared. That area, multiplied by the length and by the number of identical pieces, gives the volume of metal, and density turns the volume into kilograms.

Density starts at 7,850 kg/m³, the figure normally used for carbon and mild steel. Change it and the same geometry covers other metals: aluminium is about 2,700, titanium about 4,500, common stainless grades near 8,000 and copper about 8,960. Because mass rises in direct proportion to density, the same plate cut from aluminium weighs about 34% of its steel figure.

Shape matters in a way that is easy to misjudge by eye. A round bar holds π/4 of the metal in a square bar of the same width, so it weighs about 78.5% as much.

What the page does not cover is tube, angle, channel, I-beam or any other profile with a hollow or stepped section. Those need wall, flange and web dimensions or the producer's section tables, and running their outside sizes through as solid stock would badly overstate the weight. Drilled holes, chamfers and rolling tolerance are ignored too, so read the result as the nominal mass of plain solid bar.

What is metal weight calculator?

Metal weight here means the mass, in kilograms, of one or more identical pieces of solid straight stock: the volume of metal in them multiplied by the density of the material. Strictly, kilograms measure mass rather than weight, but the trade uses the words interchangeably and the figure is what a scale reads, what a lifting chart is checked against and what a steel merchant invoices. The net volume shown with it is the combined metal volume of all the pieces in cubic metres.

Three everyday decisions hang on the figure. A structural engineer wants the force a member puts on its supports, which is the mass times standard gravity, 9.80665 m/s²: the 31.4 kg pair of bars in the worked example bears down with about 307.93 newtons. A buyer often has to reconcile a stock list priced by the metre with an invoice priced by the kilogram; set the length and the quantity to 1 and the result is the kilograms per metre that links the two prices. And whoever moves the steel can compare it with the NIOSH lifting equation, whose starting load constant under ideal conditions is 23 kg: a single 15.7 kg flat bar is under it, while a 147 kg sheet of 6 mm plate is several times over and needs a lifting aid.

How to use this calculator.

1. 01Choose Plate / rectangular bar for sheet, plate, flat bar and square bar, or Round bar for solid rod and shafting.
2. 02Enter the length and the width or diameter in metres. Drawings are usually dimensioned in millimetres, so divide by 1,000: a 50 mm flat bar is 0.05 m wide and a 25 mm rod is 0.025 m across. For inch dimensions multiply by 0.0254, the exact metres in an inch.
3. 03For plate mode, enter the thickness in metres too; 6 mm plate is 0.006. Round-bar mode ignores the thickness field, so whatever it holds does not affect the answer.
4. 04Keep 7,850 kg/m³ for ordinary steel, or replace it with your metal's density, ideally from the supplier's data sheet for alloys such as brass or bronze. Common aluminium alloys sit within a few percent of 2,700, so that figure serves when the exact grade is unknown.
5. 05Set the number of identical pieces, then read the total mass and the net volume beneath it.

The formula.

Mass = A × L × n × ρ. A is the cross-sectional area in square metres, L the length of one piece in metres, n the number of pieces and ρ the density in kg/m³. For a plate or rectangular bar A = w × t, width times thickness; for a round bar A = π × (d ÷ 2)², which equals π/4 × d². The product A × L × n is the volume reported in cubic metres, and multiplying it by ρ gives kilograms.

Almost everything scales in a straight line: double the length, the piece count, the width, the thickness or the density and the mass doubles. Diameter is the exception. Because the area depends on its square, doubling a round bar's diameter quadruples its mass, and a 25 mm rod keyed in as 0.25 m instead of 0.025 m comes out a hundred times too heavy. The same square law magnifies measuring error: a diameter read 1% high gives a mass about 2% high, which is why round bar is better measured with callipers than with a tape.

At 7,850 kg/m³ the formula collapses into three shop shortcuts: steel plate weighs 7.85 kg per square metre for each millimetre of thickness, steel flat bar weighs 0.00785 × w × t kg per metre with both sizes in millimetres (50 × 6 mm flat is 2.355 kg/m), and steel round bar weighs about 0.00617 × d² kg per metre with d in millimetres.

Behind the formula sit three assumptions. The cross-section is the same along the whole length, so a tapered, forged or stepped part has to be split into simple prisms and the pieces added. The density is uniform, which holds for rolled bar and plate but not for a casting with internal porosity. And the rectangle has sharp corners, whereas hot-rolled flat bar has slightly rounded edges, so small flats come out a fraction heavy. Dimensional tolerance outweighs all three: a plate that rolls 0.3 mm over a nominal 10 mm carries 3% more steel than the arithmetic says.

Picking between steels moves the answer less than people expect. Common stainless grades at about 8,000 kg/m³ weigh only 1.9% more than carbon steel at 7,850, while swapping steel for aluminium removes about two-thirds of the mass. For imperial work, 7,850 kg/m³ is the same density as about 490 lb/ft³ or 0.2836 lb/in³, the figures US steel tables commonly use.

A worked example.

Frequently asked questions.

References& sources.

1. [1]National Institute of Standards and Technology. NIST SI Guide, 2008 edition. Appendix B unit relationships. Retrieved 2026-08-06.
2. [2]OpenStax, Rice University. University Physics, 2016. Volume 1 mechanics and Volume 2 thermodynamics. 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.