Steel Weight Calculator Formula
Understand the math behind the steel weight calculator. Each variable explained with a worked example.
Formulas Used
Weight per Metre
weight_per_m = pi * pow(d_m, 2) / 4 * 7850Total Weight
total_weight = pi * pow(d_m, 2) / 4 * 7850 * lengthQuick Check (D^2/162)
quick_formula = pow(diameter, 2) / 162Variables
| Variable | Description | Default |
|---|---|---|
diameter | Bar Diameter(mm) | 12 |
length | Total Length of Bars(m) | 100 |
d_m | Derived value= diameter / 1000 | calculated |
How It Works
Steel Bar Weight Calculation
Steel weight is calculated from the cross-sectional area, length, and density.
Formula
Weight per metre = (pi/4) x D^2 x rho
where D is the bar diameter in metres and rho is steel density (7850 kg/m^3).
Quick Formula
Weight (kg/m) = D^2 / 162 (where D is in mm)
This handy shortcut comes from simplifying pi/4 x (D/1000)^2 x 7850.
Worked Example
100 metres of 12 mm diameter rebar.
- 01Weight per metre = pi/4 x (0.012)^2 x 7850 = 0.888 kg/m
- 02Quick check: 12^2 / 162 = 144/162 = 0.889 kg/m
- 03Total weight = 0.888 x 100 = 88.8 kg
Frequently Asked Questions
What are standard rebar sizes?
Metric: 6, 8, 10, 12, 16, 20, 25, 32, 40 mm. US/Imperial: #3 (10mm), #4 (13mm), #5 (16mm), #6 (19mm), #7 (22mm), #8 (25mm), #9 (29mm), #10 (32mm), #11 (36mm).
How do I calculate the number of bars?
Total length = number of bars x bar length + lap splice allowances. Add 10-15% for waste, bends, laps, and cutting losses.
Does this formula work for other steel shapes?
For round bars, yes. For structural sections (I-beams, channels), use the weight per metre from manufacturer tables, as the cross-section is not a simple circle.
Ready to run the numbers?
Open Steel Weight Calculator