Steel bars are specified by size but bought and sold by weight. If you know the weight per metre, you can turn a drawing into a purchase order, check a delivery against the invoice, and estimate freight before the truck arrives. This guide gives you the formulas, a ready weight chart for common bright bar sizes, and worked examples you can use straight away.

Why bar weight matters when you order

• Pricing: bright bars are quoted per kg or per tonne, so weight decides cost.

• Quantity planning: you need weight to convert '500 pieces of 3 m' into tonnes, or the other way round.

• Receiving checks: a quick weight check at the gate tells you whether the bundle matches the invoice.

• Logistics: freight and handling are planned by weight.

The basic formula

Every bar weight calculation uses the same idea: weight equals cross-section area multiplied by length and by the density of steel. Carbon and low alloy steel has a density of about 7,850 kg per cubic metre (7.85 g/cm3). With sizes in millimetres and weight in kg per metre, the formulas simplify to the ones below.

Round bright bar weight formula

Weight (kg/m) = D x D x 0.006165, where D is the diameter in mm.

Example: a 25 mm round bar weighs 25 x 25 x 0.006165 = 3.853 kg per metre. A 3 m length therefore weighs about 11.56 kg.

Square bright bar weight formula

Weight (kg/m) = A x A x 0.00785, where A is the side of the square in mm.

Example: a 20 mm square bar weighs 20 x 20 x 0.00785 = 3.14 kg per metre. A 6 m length weighs about 18.84 kg.

Hex bright bar weight formula

Hex bars are measured across flats (AF), the distance between two opposite flat faces, which is also the spanner size. Weight (kg/m) = AF x AF x 0.0068.

Example: a 24 mm AF hex bar weighs 24 x 24 x 0.0068 = 3.916 kg per metre. A 3 m length weighs about 11.75 kg.

Bright bar weight chart (kg per metre)

Values are theoretical, calculated at 7.85 g/cm3. For sizes not listed, use the formulas above.

Converting weight into number of bars

Number of bars = order weight (kg) / (kg per metre x bar length in m).

Example: you order 1 tonne of 16 mm round bar in 3 m lengths. Each bar weighs 1.578 x 3 = 4.734 kg, so 1,000 / 4.734 = about 211 bars.

Why actual weight can differ slightly from the chart

• Size tolerance: a bar drawn to the lower side of its tolerance weighs a little less. Bright bars held to h9 or h11 sit very close to nominal size, which is why their weights match the chart closely. Hot rolled bars have wider tolerances and can vary more.

• Grade: most carbon and alloy steels sit close to 7.85 g/cm3. Stainless steels are slightly denser, so use a higher factor for them.

• Cut length: bars cut longer or shorter than ordered change the bundle weight.

• Hex corners: hex bars have small rounded corners, so real weight is marginally lower than the sharp-corner formula.

Using weight to check a delivery

When a bundle arrives, count the bars, measure a few lengths and weigh the bundle. Multiply the number of bars by the length and the chart weight per metre. If the actual weight is within a percent or two of that figure, the delivery matches. A larger gap usually means short lengths, undersize bars or a miscount, and it is worth checking a few diameters with a micrometer before you accept the load.

Frequently asked questions

• How do you calculate the weight of a round bar per metre?

  Square the diameter in mm and multiply by 0.006165. The answer is in kg per metre. For example, a 12 mm bar weighs 12 x 12 x 0.006165 = 0.888 kg/m.

  
  

• What is the weight of a 25 mm bright bar per metre?

  A 25 mm round bright bar weighs about 3.85 kg per metre. A 25 mm square bar weighs about 4.91 kg per metre.

  
  

• Is bright bar weight different from hot rolled bar weight?

  For the same nominal size and grade, the theoretical weight is the same. In practice, bright bars are closer to their nominal size because cold drawing gives tighter tolerance, so their actual weight matches the chart more closely.

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