Rebar Weight Calculator NZ
This calculator works out the weight of reinforcing steel, or rebar, from the bar diameter, the length of each bar and the number of bars. Rebar is the ribbed steel bar embedded in concrete to give it tensile strength, and it is ordered and priced by weight, so knowing how much your bars weigh is essential for estimating, ordering and handling. The weight depends almost entirely on the diameter, since steel has a consistent density, and there is a neat rule that gives the weight per metre directly from the diameter in millimetres. This tool applies it. You enter the bar diameter in millimetres, the length of each bar in metres, and the number of bars, and the calculator returns the total weight, the weight per metre for that diameter, the weight of a single bar, and the bar count. The results update as you type. Use it to estimate the steel for a slab, footing, beam or column, to price an order, or to work out handling and transport loads. The weight per metre is the diameter in millimetres squared, divided by about 162.2, a constant that comes from the cross-sectional area of the bar and the density of steel, around 7,850 kilograms per cubic metre. So a 12 millimetre bar weighs about 0.888 kilograms per metre, a 16 millimetre bar about 1.58, and a 20 millimetre bar about 2.47. Multiplying the weight per metre by the length per bar and the number of bars gives the total. This rule is widely used on site and in estimating because it needs only the diameter. As a guide, common reinforcing sizes in New Zealand are 10, 12, 16, 20 and 25 millimetres, and ordering a little extra for laps, offcuts and waste is sensible.
Weight per metre = diameter² / 162.2 (diameter in mm), from the steel density of ~7,850 kg/m³. Total = per metre x length x bars. Order extra for laps and waste.
How it works
The weight per metre of a round steel bar is its diameter in millimetres squared, divided by 162.2, a constant derived from the cross-sectional area and the density of steel. Multiplying this by the length of each bar gives the weight per bar, and multiplying by the number of bars gives the total weight.
Worked example
For 12 millimetre bars, the weight per metre is 12 squared, which is 144, divided by 162.2, about 0.888 kilograms per metre. A 6 metre bar therefore weighs about 5.33 kilograms, and 20 such bars weigh about 106.5 kilograms in total.
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