Metal densities and weight formulas

November 3, 2026  ·  Indumor

A steel round bar weighs 0.006165 · d² kilograms per meter, with d in millimeters: a 20 mm bar is 2.47 kg/m, a 50 mm bar 15.4. Plate weighs 7.85 · e kilograms per square meter, with the thickness e in millimeters: 3 mm plate is 23.55 kg/m². And any solid part weighs its volume in dm³ times 7.85. Those three sums answer nearly every "how much does this weigh" asked in a shop. The rest of the chapter is where they come from, how they adapt to other sections and other metals, and the density table for when the material is not steel.

Where 0.006165 comes from

Carbon steel has a density of 7.85 kg/dm³ (7850 kg/m³, or 0.2836 lb/in³), and that number rules every formula. A meter of round bar is a cylinder: section area times length. The area is π · d²/4 in mm²; times 1000 mm of length gives mm³; divided by a million it becomes dm³, and times 7.85, kilograms. Fold the constants together and you get π/4 × 7.85 / 1000 = 0.006165, so the sum reduces to squaring the diameter. Square bar has no π/4, which is why its constant is a bare 0.00785; a hexagon has an area of 0.866 times the across-flats squared, which gives the 0.0068. Alloy steels and stainless weigh nearly the same (304 is 7.9), so for estimating, 7.85 does for all of them.

Weight per meter of each section

The pipe formula comes from unrolling the ring: π times the mean diameter (D − e) times the wall e, and the constant π × 7.85 / 1000 = 0.02466 is the one EN 10220 uses. The square and rectangular tube formulas ignore the corner radii and come out 3 to 4 % over the catalog: a 50 × 50 × 3 gives 4.43 kg/m by the formula and 4.25 in the EN 10219 table. The angle formula runs about 1 % under, because it leaves out the root radius. All of them are fine for estimating; for settling a purchase the standard's table rules, since that is the figure on the supplier's delivery note.

Rolled sections, pipe and plate have their weights tabulated size by size in the tables section: steel bar weights, sheet metal gauges, pipe schedules and IPN beams. The formulas here are for the size that is not in the table and for checking a delivery note by hand.

Density and properties of the metals

Besides density, the table carries the other four properties a shop needs now and then. The melting point says what can be welded, cast or cut with what. The expansion coefficient is what makes a 1 m aluminum shaft grow 0.24 mm with 10 °C more, and a fit measured in the morning come out different in the afternoon. Thermal conductivity explains why copper and aluminum carry the welding heat away and ask for preheat or more amperage, and why stainless, which conducts less than a third as well as carbon steel, heats up locally and distorts more. The modulus E is stiffness: for the same section, an aluminum beam deflects three times as much as a steel one, however strong the aluminum alloy, and heat treatment does not change it.

Expansion and conductivity at 20 °C. A melting range is solidus to liquidus: the alloy starts to melt at the first and is fully liquid at the second. Melting of stainless steels and cast irons: indicative. Cemented carbide: typical values, they vary with the cobalt and the maker.

What is not metal

To price a concrete base, to know whether an empty tank floats in the water table, to work out what a hopper full of soybeans or a quebracho hatch weighs, you need the densities of what surrounds the steel. They go in kg/dm³ like the rest: the number is the same in t/m³, and times 1000 it is kg/m³.

Typical values: wood, soils and bulk materials vary a good deal with moisture, origin and compaction.

Weight of parts: cylinders, rings, spheres and cones

For a solid part the sum is volume times density. With the dimensions in millimeters the volume comes out in mm³ and has to be divided by a million to get dm³; the constants in the third column already have that division built in for steel.

Weight calculator

Quick table: round bar from 6 to 100 mm

Computed with the densities from the metals table. Commercial bars come in 6 m lengths (steel also in 12 m): the weight of a bar is the value times 6. The guide on estimating steel weight explains how to go from a structural drawing to tons.

One last point of use. When the weight is for choosing the sling, the hoist or the overhead crane, round up and add what is not on the drawing: the bolts, the paint, the water left in the tank after the hydrotest. When it is for quoting, use the theoretical weight from the standard, which is the one on the supplier's delivery note.

Frequently asked questions

How much does a meter of 12 mm round bar weigh?

0.888 kg: 0.006165 × 12² = 0.888 kg/m. A 12 m bar weighs 10.7 kg and a 6 m bar 5.3 kg. In inch terms, 1/2 in round bar is 0.668 lb/ft.

How much does 3 mm plate weigh per square meter?

23.55 kg/m² (7.85 × 3). A 1500 × 3000 sheet of 3 mm plate weighs 106 kg; 2 mm plate is 15.7 kg/m² and 71 kg per sheet.

What is the density of stainless steel?

7.9 kg/dm³ for 304 and 8.0 for 316 (EN 10088-1), 1 % more than carbon steel. Aluminum is 2.7, a third of steel; bronze 8.8; lead 11.34.

Sources: ASM Handbook, vol. 2, Properties and Selection: Nonferrous Alloys and Special-Purpose Materials (1990); CRC Handbook of Chemistry and Physics; EN 10088-1 (density of stainless steels); EN 1561 and EN 1563 (cast irons); EN 1706 (aluminum); EN 10220 (mass per meter of pipe); EN 10219 and EN 10210 (structural hollow sections); EN 10056-1 (angles).