Practical guide
Rebar Weight per Metre: Formula and Diameters
Use nominal diameter and density or a confirmed kg/m rate to estimate reinforcing-bar mass without confusing length, bar labels and strength.
Updated 16 October 2026
Reviewed by the 99Tools team. Editorial and corrections policy.
Use nominal diameter and the right units
For the circular-area estimate, convert nominal diameter from millimetres to metres, square it, multiply by π/4, then multiply by reference density. The result is kg per metre of bar. The calculator starts at 7850 kg/m³ as a reference steel density and makes that input editable. Confirm the actual product data where an applicable standard, supplier schedule or billing basis requires its published mass rate.
The d squared over 162 shortcut
With diameter in millimetres, d²/162 is a common rounded estimating shortcut. It is close to the circular-area calculation at the reference density but not the exact same coefficient. The calculator keeps the full π-based calculation until display rather than mixing rounded kg/m values into an exact nominal result. A published table can also use rounded values or a specified nominal product rate, so very small differences do not automatically mean two tools use different diameters.
Y10, Y12, Y16 and Y20 mass
At the reference density, the nominal estimates are about 0.617, 0.888, 1.578 and 2.466 kg/m for 10, 12, 16 and 20 mm diameters respectively. Multiply the unrounded rate by scheduled metres for the model result. Y or T notation should be checked against the actual product and project identification; a letter alone does not prove grade, permitted substitution or a complete standard specification.
From one metre to a full schedule line
A hypothetical nominal 12 mm bar has about 5.327 kg per 6 m piece in this model. Twenty pieces represent 120 m and about 106.538 kg before any extra allowance. Do not round each metre or piece to whole kilograms before adding the schedule. Also distinguish a 10 m bar length from a 10 mm diameter: the length alone does not identify unit mass.
US number-four bar is a different designation
A US #4 bar has a nominal diameter of 0.500 inch, which converts to 12.7 mm. It does not mean 4 mm and is not an automatic substitute for a 12 mm South African bar. The diameter model gives about 0.994 kg/m at the reference density, but applicable published nominal tables or supplier rates should govern the required specification and procurement basis. Enter a confirmed kg/m rate when that is the appropriate method.
Mass and capacity answer different questions
Kilograms per metre describe material quantity. They do not determine the safe load a bar or reinforced member can carry. Grade, concrete, anchorage, support geometry, detailing and the loading arrangement matter. A heavier nominal bar or equal total steel mass is not by itself an approved substitution. Use the specified reinforcement design and treat this calculator as a mass take-off.
Use the related calculators
Apply the explanation above with your own figures. Open a calculator below, check every input and review the result assumptions before making a decision.
Frequently asked questions
What is the nominal rebar mass formula?
π/4 × diameter in metres squared × reference density gives kg/m.
Why does d²/162 differ slightly from the model?
It is a rounded shortcut. The model retains π and the entered density.
Is US #4 the same as 4 mm?
No. Its nominal diameter is 12.7 mm.
Does kg/m show how much load rebar can hold?
No. Structural capacity needs a complete design assessment.