Rebar Weight Calculator
Estimate the total weight of reinforcement bars from three inputs: bar diameter in millimetres, bar length in metres, and quantity. The tool opens with 12 mm, 6 m and 10 bars, which matches a standard stock length, and updates the total in kilograms as you change any value.
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Rebar Weight Calculator online
Work out the total weight of straight reinforcing bars from the diameter, bar length and count, using the standard d²/162 unit-weight rule — for ordering, delivery checks and bending-schedule estimates.
How it works
The calculator uses the site-standard d²/162 rule, which gives the weight of one metre of steel bar directly from its diameter: kg per metre = diameter(mm) × diameter(mm) / 162. The constant 162 combines the cross-sectional area of a round bar (π/4 × d²) with the density of steel (7850 kg/m³), so you never need to convert millimetres to metres yourself. Total weight is then (d²/162) × length(m) × quantity. Diameter must be entered in millimetres while length is in metres; mixing those units is the most common error.
Worked example
Take 20 bars of 16 mm rebar, each 12 m long. Unit weight = 16 × 16 / 162 = 256 / 162 = 1.5802 kg/m. One 12 m bar weighs 1.5802 × 12 = 18.963 kg. For 20 bars: 18.963 × 20 = 379.3 kg. With the tool defaults (12 mm, 6 m, 10 bars): 12 × 12 / 162 = 0.8889 kg/m, one bar = 0.8889 × 6 = 5.333 kg, total = 5.333 × 10 = 53.33 kg.
Units
Output is in kilograms. Divide by 1000 for tonnes (379.3 kg = 0.379 t). Common unit weights worth memorising: 10 mm = 0.617 kg/m, 12 mm = 0.889 kg/m, 16 mm = 1.580 kg/m, 20 mm = 2.469 kg/m, 25 mm = 3.858 kg/m.
Practical tips
- Count laps and hooks separately. A 12 m stock bar cut into shorter pieces still weighs the same per metre, but lap lengths add extra metres you must include in the length or quantity.
- Round bar schedules up to whole bars. If the math says 19.4 bars, order 20 and let offcuts cover chairs and spacers.
- Check whether your supplier bills theoretical weight (d²/162) or actual weighbridge weight; rolled bars can run a few percent lighter than theory.
- This estimate covers material quantity only. Bar sizes, spacing, laps and cover must follow the structural drawings and be checked by a qualified engineer before fixing steel.
Edge cases and limitations
- Laps are invisible steel. The result counts the bars you list; the laps that join them are extra. A typical lap runs 40–60 bar diameters — 640–960 mm on a 16 mm bar — so a long wall or slab detailed with many laps can carry 3–8% more steel than the net bar list suggests. Add laps to the count before ordering.
- Cutting plans beat percentages. Stock comes in fixed lengths (commonly 12 m). Cutting 5.5 m bars from 12 m stock wastes 1 m per stock bar unless the offcuts pair up elsewhere in the schedule. A cutting plan usually saves more than the generic waste allowance costs.
- Bends consume length. The length in the schedule is the cut length along the bar's centreline, not the sum of the finished shape's outside dimensions — hooks and bends are already accounted for in standard shape codes. Measuring a bent bar with a tape and re-entering the sum double-counts the bends.
- Coatings change bond, not weight. Epoxy-coated and galvanized bars weigh essentially the same as black bar (the coating is a fraction of a percent), but design codes often demand longer laps for coated bars — the weight effect arrives through the lap length, not the unit weight.
Privacy and browser processing
The calculation runs entirely in your browser — your figures are never uploaded.
Frequently asked questions
Where does the 162 in d²/162 come from?
It folds the area of a circle (π/4 × d²) and the density of steel (7850 kg/m³) into one divisor with millimetre-to-metre conversion built in. For a 12 mm bar: 12 × 12 / 162 = 0.8889 kg per metre, which matches the exact area × density calculation.
How much does a 12 m length of 16 mm rebar weigh?
Unit weight is 16 × 16 / 162 = 1.5802 kg/m, so one 12 m bar weighs 1.5802 × 12 = 18.96 kg. Ten such bars total about 189.6 kg.
Should I enter radius or diameter?
Always the nominal bar diameter in millimetres (10, 12, 16, 20 and so on). Entering the radius gives roughly one quarter of the true weight because the formula squares the input.
Does the result include cutting waste?
No. The tool multiplies exact length by quantity, so add 3–5% for cutting waste, short offcuts and laps, and round up to whole stock lengths (commonly 6 m or 12 m) when ordering.