Rebar Length Calculator
The total linear length is simply the number of bars multiplied by the cut length of each bar, where the cut length is the design length plus any lap (splice) allowance you add per bar: total = bars x (length + lap).
Enter Values
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the number of bars and the length of each bar in metres.
- Optionally add a lap allowance per bar (m) so splices are included in the ordered length.
- Optionally enter the bar diameter (mm) to also get mass per metre and total weight.
How it works
The total linear length is simply the number of bars multiplied by the cut length of each bar, where the cut length is the design length plus any lap (splice) allowance you add per bar: total = bars x (length + lap). This gives the running metres of reinforcement to order for the run.
When a bar diameter is supplied, mass per metre is taken from the standard steel relationship kg/m = 0.00617 x d^2 (d in mm), which is the metric equivalent of d^2/162. Total mass = total length x mass per metre. This is a straightforward ordering estimate — it does not add bar bends, hooks, stock-length offcuts or wastage, which you should allow for separately on the reinforcement schedule.
Worked example
50 bars at 6 m with a 0.4 m lap, 12 mm diameter. Enter 50 bars, 6 m per bar, a 0.4 m lap allowance per bar and a 12 mm diameter. Cut length per bar = 6 + 0.4 = 6.4 m, so total rebar length = 50 x 6.4 = 320 m. Mass per metre = 0.00617 x 12^2 = 0.888 kg/m, giving a total mass of 320 x 0.888 = 284.4 kg. That is the linear metres and weight to order for this run of bars.
Common mistakes
- Forgetting to include a lap allowance per bar, which under-orders reinforcement where bars are spliced end to end.
- Confusing total length with the number of stock lengths — suppliers sell fixed stock lengths, so round up and allow for offcuts separately.
- Mixing units: length must be in metres and diameter in millimetres; entering diameter in metres will give a nonsensical mass.
Frequently asked questions
Does this include laps and wastage?
Laps are included only if you enter a lap allowance per bar. The tool does not add wastage, offcuts or bar bends automatically — allow for those separately based on your schedule and supplier stock lengths.
How is the mass per metre calculated?
It uses the standard steel formula kg/m = 0.00617 x d^2, where d is the bar diameter in millimetres. For a 12 mm bar that is about 0.888 kg/m, matching the common d^2/162 rule.
Is the number of bars rounded?
No. The number of bars must be a whole number you enter — the tool multiplies it directly by the cut length per bar. It does not calculate how many bars a slab or member needs.
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