How to Calculate Rebar Weight and Cutting Length

Updated 5 October 2026 · العربية

Two numbers decide every steel order: how much a bar weighs, and how long it must be cut. This page gives the formula for the first, the principle for the second, and a worked example.

Weight of a reinforcing bar

Steel weighs about 7850 kg per cubic metre, so the weight per metre of a round bar of diameter d (in millimetres) is:

weight (kg per metre) ≈ d² ÷ 162

The table below uses d² ÷ 162.2, which matches the unit weights printed in most steel catalogues.

Worked example

20 bars of 16 mm, each cut to 6.5 m:

• Weight per metre of 16 mm = 16² ÷ 162.2 = 1.578 kg/m
• Weight of one bar = 1.578 × 6.5 = 10.26 kg
• Weight of 20 bars = 10.26 × 20 = 205.2 kg

Always add the weights of every bar mark per diameter: steel is bought and priced by diameter and length.

Cutting length

The cutting length is the length of the straight bar before it is bent. For a straight bar it is simply its length. For a bent bar it is the sum of the straight parts of the shape, corrected at every bend and at every hook:

• Dimensions on drawings and in bar schedules are usually measured to the outside of the bar, so the sum of the dimensions is longer than the steel really is. A deduction is made at each bend; its size depends on the bar diameter and the bend angle.
• Hooks and bar ends add an allowance that also depends on the diameter.
• The exact deductions and allowances are different in BS 8666, ACI and other standards, so always use the formula of the standard your project follows.

Unit mistakes to avoid

• Diameter in millimetres, length in metres: the formula above gives kg per metre.
• Do not mix millimetre schedules with feet-inch drawings; convert once and write it down.
• Check the total in tonnes against a rule of thumb for the member type before the order goes out.

Let the program do it

BarFlow BBS calculates the cutting length and the weight of every bar automatically for each ready-made shape, draws the shape with its dimensions, and totals the weight by diameter. Try it free: the free version has 30 ready shape codes, up to 20 rows and one bar diameter (12 mm).

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