Rebar Weight Calculator
Calculate the weight of reinforcement bars from diameter, length and quantity.
Formula
Weight per metre = cross-sectional area × steel density. The familiar d² ÷ 162 shortcut is this same formula with the density fixed at 7850 kg/m³.
- Area (m²) = π × (d ÷ 2)²
- Weight per metre (kg/m) = Area × Density
- Shortcut (metric): kg/m ≈ d² ÷ 162, with d in mm
- Total (kg) = kg/m × Bar length × Number of bars × (1 + wastage % ÷ 100)
Worked example
50 bars of 16 mm diameter, 12 m long, at 7850 kg/m³ with 5% wastage.
- Area = π × (0.008)² = 0.000201 m²
- Weight per metre = 0.000201 × 7850 = 1.58 kg/m
- Check with the shortcut: 16² ÷ 162 = 1.58 kg/m
- One bar = 1.58 × 12 = 18.95 kg
- Net = 18.95 × 50 = 947.5 kg
- With 5% wastage = 994.9 kg
About 995 kg, just under one tonne.
Assumptions and limitations
- Nominal diameter is used. Deformed bars have ribs, but weight is conventionally calculated on the nominal diameter, which is how bar bending schedules and mill certificates work.
- Steel density of 7850 kg/m³ is the standard convention for carbon steel reinforcement. It is editable in case your standard differs.
- Bar length is the cut length. Bends and hooks add length that should already be in your bar bending schedule.
- Wastage covers offcuts and site losses; it does not cover laps unless your schedule omits them.
What this calculator does not do
- Does not design reinforcement. Bar size, spacing, laps, anchorage and cover are structural design outputs.
- Does not produce a bar bending schedule or work out bend allowances. Enter cut lengths that already include bends and hooks.
- Does not cover mesh, couplers, spacers, tying wire or chairs, which are ordered separately.
Practical tips
- Learn the d² ÷ 162 shortcut. It gives kilograms per metre for any metric bar diameter and lets you sanity-check a delivery note in your head.
- Check whether your bar bending schedule already includes laps. Adding a lap allowance on top of a schedule that includes them is a common over-order.
- Reconcile weighbridge tickets against the schedule as steel arrives. Reinforcement discrepancies are far easier to resolve before the bars are fixed.
Frequently asked questions
What is the weight of 16 mm rebar per metre?
About 1.58 kg/m at a steel density of 7850 kg/m³. You can get this from the full formula or from the d² ÷ 162 shortcut — both give the same answer.
Where does the d² ÷ 162 formula come from?
It is the cross-sectional area times the density, rearranged. π/4 × d² in mm², converted to metres and multiplied by 7850 kg/m³, works out to d² ÷ 162.28. The rounded 162 is close enough for site use.
Should I use nominal or actual diameter?
Nominal. Bar bending schedules, mill certificates and suppliers all work on nominal diameter, so using anything else will put your figures out of step with the paperwork.
How much wastage should I allow on reinforcement?
Typically 3–7%, depending on how much cutting is involved and whether your schedule already accounts for laps. Complex detailing with many short bars generates more offcuts.
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Estimating tool, not a design. This calculator works out quantities from the dimensions you enter. It does not size any structural member, verify a design, or confirm compliance with any building code. Check every result against your project specification and applicable local standards, and involve a qualified engineer where the work requires one.