How the weight is worked out
The cross-sectional area is calculated from the shape, multiplied by the length to give a volume, then multiplied by the density of steel.
A round bar uses pi over four times the diameter squared. A square bar uses the side squared. A flat uses the width times the thickness.
A 20 mm round bar one metre long has a cross-section of 314 square millimetres, which is 0.000314 cubic metres over a metre, and weighs 2.466 kg.
Worked example
A 20 mm round bar one metre long weighs 2.466 kg, so a six metre length weighs 14.8 kg.
A flat bar 100 mm by 10 mm is 1,000 square millimetres of section, which is 0.001 cubic metres per metre and 7.85 kg per metre.
What this does not tell you
The weight is the nominal weight from the dimensions. Rolled sections carry a tolerance, and a bar that is slightly under size weighs slightly less.
Structural sections such as universal beams and columns are quoted as a mass per metre by the manufacturer, and that figure already accounts for the root radii that this calculation ignores.
Weight is not the same as safe working load. A lifting plan needs the rigging, the centre of gravity and a rated sling, not just the mass.
Limits of this calculator
It covers round, square and flat sections only. Angles, channels, beams and hollow sections have their own published masses.
It uses one density for all steel. Stainless and some alloys differ by a few per cent.
It does not calculate the weight of a fabricated assembly, which needs each part added and the welds allowed for.
For another material weight, use the glass weight calculator.
Inputs for the steel weight calculator
Section
Round bar, square bar or flat. The shape decides which dimensions are used.
Length
Length of the bar or plate in metres.
Width or diameter
Diameter for a round bar, side for a square, width for a flat.
Thickness
Only used for a flat bar or plate. Ignored for round and square sections.
CALCULATOR QUESTIONS
Steel weight calculator questions
How much does a 20 mm steel bar weigh?
2.466 kg per metre, so about 14.8 kg for a six metre length.
What is the density of steel?
About 7,850 kg per cubic metre, or 7.85 grams per cubic centimetre.
Does this work for stainless steel?
Approximately. Stainless is around 8,000 kg per cubic metre, so add about 2 per cent.
Can I use it for a beam?
No. Universal beams are quoted by mass per metre, which already allows for the root radii this calculation ignores.