How to work out the weight of steel plate by hand

The rule

Weight = volume × density. Work in one set of units: millimetres and kg/m³ (divide the volume in mm³ by 10⁹ to get m³), or inches and lb/in³. Carbon steel is printed as 0.2833 lb/in³ in NBS Circular 391 (1931), p. 4 — 7841.7 kg/m³; stainless 304/316 is 0.286 lb/in³ (MIL-HDBK-5J (2003, cancelled), Table 2.7.1.0(b), p. 2-223); aluminium 6061 is specific gravity 2.7 (TO 1-1A-9, Table 3-6, p. 3-18). Real plate is rolled to a thickness tolerance, which often matters more than the density.

1. A plate

A 2400 × 1200 × 6 mm steel plate: volume 2400 × 1200 × 6 = 17,280,000 mm³ = 0.01728 m³, times 7841.7 kg/m³ = 135.5 kg. The quick way: steel plate weighs about 7.84 kg per square metre per millimetre of thickness, so 2.88 m² × 6 mm × 7.84 gives the same.

2. A disc or ring

The area is π ÷ 4 × (outside² − inside²). A 600 mm disc with a 200 mm hole, 6 mm thick: π ÷ 4 × (600² − 200²) × 6 = 1,507,964 mm³, so 11.8 kg. Work from the 600 × 600 square it is cut from and you get 16.9 kg — the weight of the plate you buy, not of the ring you ship.

3. A tube

The cross-section is π × wall × (outside diameter − wall). A 6 m length of 114.3 × 6.02 mm steel tube: π × 6.02 × (114.3 − 6.02) × 6000 = 12,287,000 mm³, so 96.4 kg, or 16.06 kg per metre.

In inches

0.2833 lb/in³ × 144 in² = 40.8 lb per square foot per inch of thickness, so ¼ in steel plate is about 10.2 lb/ft². For comparison, the 1893 sheet-gauge law was built on wrought iron at 40 lb/ft² per inch, while today’s steel gauge column follows about 41.82 (an observed pattern, see the gauge chart) — so density explains only part of why the old gauge thicknesses and steel’s differ.

Common mistakes

• Mixing millimetres with kg/m³ without the 10⁹ — the answer comes out a billion times off.
• Forgetting to subtract the hole of a ring, or using the outside diameter alone for a tube.
• Using the steel density for aluminium: it is about a third of the weight. (Stainless is only about 1 % heavier than steel.)
• Forgetting the thickness tolerance when a weight has to be guaranteed.

How this matches the tool

The metal weight calculator does plate, discs, tube and bar for these materials and a custom density. The worked numbers on this page were produced by its code, with its cited densities, when the page was built.

Sources

1. NBS Circular 391, Standard Thicknesses, Weights, and Tolerances of Sheet Metal (1931), p. 4: steel 489.6 lb/ft³ = 0.2833 lb/in³
2. MIL-HDBK-5J (2003, cancelled), Table 2.7.1.0(b), p. 2-223: stainless 304/316 0.286 lb/in³
3. TO 1-1A-9, General Shop Practice, Table 3-6, pp. 3-17–3-18: aluminium alloy specific gravities (6061: 2.70)
4. Act of March 3, 1893 (27 Stat. 746), 15 U.S.C. §206 (US Code 2024, govinfo): sheet gauges defined by weight; the thicknesses are the weight at 40 lb/ft² per inch, wrought iron at 480 lb/ft³ (NBS Circular 391, p. 4)