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Metal Weight Calculator

Calculators · By Sidhin · Added

Mass is volume times density, and both halves are easy to get subtly wrong: the cross-section of a hex bar and an angle are not what people guess, and 'steel' covers a four per cent spread of densities. Pick the profile and the alloy and both are handled.

Cross-section = π × (d ÷ 2)²

How to use the metal weight calculator

  1. 1Choose the profile — the fields change to match, and the formula for its cross-section is shown.
  2. 2Pick the alloy, or enter a density from a specification sheet.
  3. 3Enter the section dimensions and the length, each with its own units.
  4. 4Set the quantity to get the weight of a whole order alongside the per-piece figure.

Examples

Mild steel round bar

Input
25 mm diameter, 6 m long
Result
23.13 kg per length · 3.85 kg per metre

Aluminium square tube

Input
50 mm outside, 3 mm wall, 2.4 m, 6061
Result
3.65 kg each · 21.9 kg for six

About the metal weight calculator

The cross-sections that catch people out

An equal angle is not two rectangles. Two legs of length L and thickness t overlap in a t × t square at the corner, so the area is 2Lt − t², and forgetting the subtraction counts that corner twice. On a small angle with a thick leg the error is several per cent.

A hexagon is not a circle either, though it is often estimated as one. Its area is about 8% less than the circle that would just contain it and about 65% of the square across the flats — near enough to a circle to make the estimate tempting and far enough to matter on a quantity.

Per metre is the number to remember

Stock is specified by weight per unit length: a supplier's catalogue lists kilograms per metre or pounds per foot for every size they carry. That figure depends only on the section and the material, not on how long a piece you cut.

It is worth taking from the result and keeping, because it converts any future length in one multiplication, and because it is the figure to check a catalogue against. A per-metre weight that disagrees with the supplier's usually means the density assumed here is not the alloy they are quoting.

Frequently asked questions

Which dimension does a hex bar use?
Across the flats — the one callipers give you, and the one hex bar is sold by. Its area is (√3 ÷ 2) times that dimension squared. Using the across-corners measurement instead overstates the area by a third, and it is the most common way this particular calculation goes wrong.
Why does the alloy matter so much?
Because it moves the answer more than most people expect. Plain carbon steel is about 7,850 kg/m³ and stainless 304 is about 8,000 — a two per cent difference that is larger than the rolling tolerance on the stock. Aluminium is roughly a third of steel, and lead is nearly half again heavier. Guessing 'steel' when the material is stainless puts every figure out.
Is the tube calculation for outside or inside diameter?
Outside diameter plus wall thickness, which is how tube and pipe are specified. The bore is the outside diameter less twice the wall, and the area is the difference between the two circles. The tool refuses a wall thick enough to close the bore rather than returning a negative area.
How accurate is the result?
It is exact for the dimensions and density you enter and nominal for the real thing. Stock carries a rolling tolerance on every dimension, and square tube and angle are calculated on sharp corners where the real section has a radius — which puts the true weight a per cent or so below these figures on thin wall. For a shipping declaration or a lift plan, use the mill certificate or a weighbridge.

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