The calculation, without hidden assumptions
Estimate reinforcement-bar mass from nominal diameter, cut length and count. The calculator derives unit mass from circular area × steel density, shows every substituted step, and keeps user-entered cutting/lap/waste allowance separate from the net takeoff.
How to use this calculator
Enter the nominal bar diameter shown on the drawing or bar bending schedule.
Enter cut length and whole-bar quantity; use feet/inches only when that is your source measurement.
Add a project-specific allowance only when required by your BBS/procurement method.
Optionally enter rate/kg for cost or a target mass for reverse whole-bar count.
Compare an entered measured/published kg/m value against the theoretical result without overwriting it.
Where people use it
- •Check TMT/rebar weight for a bar bending schedule or quantity takeoff.
- •Convert a diameter and cut list into kg and metric tonnes for procurement.
- •Compare kg/m and lb/ft for site or supplier documentation.
- •Estimate order mass after an explicitly entered cutting/lap/waste allowance.
- •Reverse a truck/order mass into the number of whole equal-length bars it can represent.
12 mm × 12 m × 50 bars
A 12 mm nominal round steel bar has about 113.10 mm² area and 0.8878 kg/m theoretical mass at 7,850 kg/m³. Fifty 12 m bars are about 532.69 kg net before any entered allowance.
What the result does not assume
- •This is a mass/takeoff calculator, not a reinforcement design or structural-capacity tool.
- •The familiar d²/162 shortcut is a rounded form of circular area × approximately 7,850 kg/m³; MAXScanner keeps the first-principles calculation visible.
- •Ribs, rolling tolerances and the governing product standard can make delivered mass differ from the smooth nominal-cylinder estimate.
- •Do not invent lap or wastage percentages: use the bar bending schedule, project specification or approved estimating method.
- •US bar-number nominal weights and national standards should be checked against their governing tables when procurement compliance matters.
Frequently asked questions
How do I calculate rebar weight per metre?+
For nominal diameter d in millimetres, calculate circular area πd²/4, convert mm² to m², then multiply by 7,850 kg/m³. This is approximately d²/162.2 kg/m.
Why do people use d²/162 for TMT bar weight?+
It is a convenient rounded shortcut derived from circular cross-sectional area and steel density. Small differences appear depending on whether 162, 162.2 or the full first-principles expression is used.
How much does a 12 mm rebar weigh?+
At 7,850 kg/m³, a nominal 12 mm round bar is about 0.888 kg/m, so a 12 m bar is about 10.65 kg theoretically.
Does the calculator include laps and wastage?+
Only when you enter an allowance. The net bar mass is always shown separately so a planning percentage cannot silently alter the underlying takeoff.
Can I calculate bars per tonne?+
Yes. MAXScanner reports the number of whole entered-length bars that fit within one theoretical metric tonne.
Why does weighbridge or mill weight differ?+
The calculator uses nominal diameter and density. Actual reinforcement has ribs and manufacturing tolerances, while standards may define nominal mass and permitted variation. Use certified supplier or standard data for acceptance.
Semantic next steps
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Keep the result connected to the real job
MAXScanner keeps the formula and assumptions beside the result so you can verify the number before using it in a drawing, estimate, specification, worksheet or document. Where a supplier, manufacturer, drawing or applicable standard owns a requirement, that source remains authoritative.