Rebar Weight CalculatorFree online other calculator — instant results, no sign-up
Calculate steel rebar mass using a density of 7850 kg per cubic meter.
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About the Rebar Weight Calculator
The Rebar Weight Calculator estimates the mass of steel reinforcing bar from its diameter in millimeters and total length in meters. It treats the rebar as a solid circular cylinder and uses a fixed steel density of 7850 kg per cubic meter. With the default diameter of 12 mm and total length of 100 m, the result is 88.781408 kg.
- Diameter (mm)
- The nominal diameter of the rebar in millimeters, with a default value of 12 mm.
- Total length (m)
- The combined length of all rebar of the entered diameter in meters, with a default value of 100 m.
Formula and method
m = ρ × (π/4) × (d/1000)² × L; with the defaults, m = 7850 × (π/4) × (12/1000)² × 100 = 88.781408 kg, rounded to six decimal places.
- mCalculated rebar mass in kilograms.
- ρSteel density, fixed at 7850 kg/m³.
- πPi, the constant used to calculate circular cross-sectional area.
- dRebar diameter in millimeters; dividing by 1000 converts it to meters.
- LTotal rebar length in meters.
Convert the diameter from millimeters to meters, then calculate the circular cross-sectional area as π/4 times the squared diameter. Multiply this area by the total length to obtain the steel volume in cubic meters. Multiply the volume by 7850 kg/m³ to obtain mass in kilograms.
Worked example
These are the calculator's starting values and the results it actually produces for them.
Inputs
- Diameter12 mm
- Total length100 m
Results
- Result88.781408 kg
How to use the Rebar Weight Calculator
- 1Find the nominal diameter of the rebar and enter it in Diameter (mm); the default is 12.
- 2Add together the lengths of all bars with that diameter, including any lap or cutting allowances you intend to count.
- 3Enter that combined length in Total length (m); the default is 100.
- 4Run the calculation to convert the rebar dimensions into steel mass.
- 5Read the Result in kilograms: the default inputs give 88.781408 kg.
Reading your result
The Result row shows the estimated total mass in kilograms for the full length entered, not the mass per meter or per individual bar. For 12 mm diameter rebar with a total length of 100 m, Result = 88.781408 kg. The displayed decimal places reflect numerical calculation precision, not guaranteed accuracy of the physical rebar mass.
Limitations
The calculation assumes a uniform, solid circular cross-section and a constant density of 7850 kg/m³. Actual rebar mass can differ because of manufacturing tolerances, rib geometry, steel composition, and coatings; use nominal diameter rather than measuring across the outer rib tips. Waste, laps, hooks, and bends are included only to the extent that their lengths are included in the input. Calculate different diameters separately and add their masses. This tool estimates mass only and does not determine reinforcement requirements, structural capacity, or code compliance.
Common questions
Can I enter the combined length of several rebar pieces?+
Yes, provided all pieces have the same nominal diameter. Add their lengths in meters and enter the sum as Total length (m).
Should I measure the diameter over the raised ribs?+
Use the nominal diameter specified for the rebar. Measuring over the rib tips can overstate the equivalent circular cross-section and therefore the estimated mass.
Does the calculator automatically include lap lengths and cutting waste?+
No. Include lap lengths, hooks, bends, and any cutting allowance in the total length if you want their steel mass counted.
Why does diameter have a stronger effect on mass than length?+
Mass is proportional to diameter squared because diameter determines circular cross-sectional area. At a fixed length, doubling the diameter quadruples the calculated mass; at a fixed diameter, doubling the length doubles the mass.
Does the calculator save my information?+
Calculations run in your browser. While signed in, inputs and results are automatically recorded in account history; saving a result creates a separate saved record.
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Results are estimates for informational purposes and are not financial, medical or legal advice.