Rebar Weight Calculator
Calculate the total weight of reinforcement bars (rebar) by size, length, and quantity.
Supports metric and imperial bar sizes.
Rebar (reinforcing bar) weight is calculated from the bar’s diameter and length. Knowing the weight lets you estimate material costs, transportation loads, and structural reinforcement capacity.
The Formula:
Weight (kg) = (Diameter in mm)^2 / 162 × Length (m)
This is derived from: Weight = Volume × Density where steel density = 7,850 kg/m³
Simplified: Weight per meter by bar size:
| Bar Designation | Diameter (mm) | kg per meter |
|---|---|---|
| R6 | 6 mm | 0.222 kg/m |
| R8 | 8 mm | 0.395 kg/m |
| N10 | 10 mm | 0.617 kg/m |
| N12 | 12 mm | 0.888 kg/m |
| N16 | 16 mm | 1.578 kg/m |
| N20 | 20 mm | 2.466 kg/m |
| N25 | 25 mm | 3.853 kg/m |
| N32 | 32 mm | 6.313 kg/m |
Metric bars and US bar numbers are not the same sizes. United States bar numbers count eighths of an inch, so a #4 is 4/8 inch, which is 12.7 mm. The nearest metric equivalents run 10 mm to #3, 12 mm to #4, 16 mm to #5, 20 mm to #6, 25 mm to #8, and 32 mm to #10. None of those pairs match exactly, and the 6 mm and 8 mm bars common in stirrups and ties have no US counterpart at all. Switch this calculator to imperial and it reports the true weight of the nearest US bar, so expect a small step in the number when you flip units.
Worked Example:
A slab reinforcement requires:
- 50 bars of N12 rebar, each 6 meters long
Weight per bar = 0.888 × 6 = 5.328 kg Total weight = 50 × 5.328 = 266.4 kg
Steel is bought by weight, so that 266.4 kg figure is the number your supplier quotes against. Rebar pricing swings hard with the scrap market and varies by country, so get a current quote rather than working from a remembered rate.
Practical Tips:
- Add 5 to 10% wastage for lapping, bending, and cutting losses
- Minimum lap length = 40 × bar diameter, so N12 bars need 480 mm laps
- Bar spacing in slabs is typically 150 to 300 mm center to center depending on loading
- Always verify rebar specifications against the structural engineer’s drawings. Reinforcement is not a place to guess.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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