What that piece of steel actually weighs.
Pick the shape and the material, enter the dimensions, and get the weight per piece and for the whole lot.
Weight
- Per piece
- 47.100 kg
- Density used
- 7.85 g/cm³
- Total (1 pc)
- 47.10 kg
Theoretical weight for a perfect piece. Real material sits inside a rolling tolerance — two to three percent on sheet is normal — and you are billed for what the weighbridge read.
Almost everything in a fabrication shop is bought by weight and quoted by piece. The conversion between those two sits in the middle of every enquiry, and it is done from memory more often than anybody would like to admit — which is how a quotation ends up eleven percent under the cost of the material it is made from.
The arithmetic is not hard. Volume times density, with the units kept straight. What makes it error-prone is that dimensions arrive in millimetres, density is quoted in grams per cubic centimetre, and the answer is wanted in kilograms — so there is a factor of a million sitting in the middle of it waiting to be dropped.
This handles the conversion and shows the formula, so a figure can be checked rather than trusted.
The formula
- Sheet or plate
Weight = L × W × T × Density ÷ 1,000,000- Round bar
Weight = π ÷ 4 × D² × L × Density ÷ 1,000,000- Square bar
Weight = S² × L × Density ÷ 1,000,000- Pipe or tube
Weight = π × (OD − T) × T × L × Density ÷ 1,000,000
Density is where the error usually is
Mild steel is taken as 7.85 g/cm³ and stainless as about 7.90 — close enough that using one for the other on a small job is invisible, and expensive on a large one. Aluminium at 2.70 is roughly a third of steel, brass 8.50 and copper 8.96.
Grade matters more than most quotations allow for. SS 304 and SS 316 are not the same density, and neither are the aluminium alloys. For a costing exercise the standard figures here are fine; for a large order, use the figure on the mill certificate.
Theoretical weight is not billed weight
What this calculates is the theoretical weight of a perfect piece. What arrives is within a rolling tolerance of it, and what you are billed for is what the weighbridge said. On sheet that gap is routinely two or three percent, and it is always in the supplier's favour when the tolerance is one-sided.
So use theoretical weight for quoting and for planning, and reconcile against the actual weight at goods receipt. The difference between the two, tracked over a few months, is a useful thing to know about a supplier.
Scrap is part of the weight you buy
A quotation built on the finished part's weight is short by whatever the cutting pattern wastes. On a nested job that might be eight percent; on a job with awkward geometry it can be a quarter of the sheet.
The honest number is material purchased, not material delivered — which means the quotation needs the yield, and the yield needs to have been measured on a job like this one before.
Questions people ask.
How do I calculate the weight of a steel sheet?
Length × width × thickness in millimetres, times density in g/cm³, divided by 1,000,000 to get kilograms. A 2000 × 1000 × 3 mm mild steel sheet is 2000 × 1000 × 3 × 7.85 ÷ 1,000,000 = 47.1 kg.
What is the density of mild steel?
7.85 g/cm³ is the standard figure. Stainless is about 7.90, aluminium 2.70, brass 8.50 and copper 8.96. For a large order use the figure on the mill certificate rather than the standard.
How is pipe weight calculated?
π × (outside diameter − wall thickness) × wall thickness × length × density ÷ 1,000,000. The (OD − thickness) term is the mean diameter, which is what makes this the weight of the wall rather than of a solid bar.
Why does the supplier's weight differ from this?
This is theoretical weight for a perfect piece. Real material sits inside a rolling tolerance, and you are billed for what the weighbridge read. Two to three percent on sheet is normal.
Should I quote on the finished weight?
No — quote on the material you have to buy, which includes whatever the cutting pattern wastes. Using the finished part's weight understates the job by the yield loss.
Other free tools
Doing this for every item, every day?
A calculator is the right tool once. When it is every item in the store, it belongs in the system that already knows the numbers.