Rebar Weight Calculator
Work out the weight of reinforcing bars from the bar size, length and number of bars, for metric (mm) and imperial (#) bar sizes.
The formula
Weight per meter in kg = d² ÷ 162, where d is the bar diameter in millimeters. It comes from the area of the circle times the density of steel: π ÷ 4 × d² mm² × 7,850 kg/m³ is about d² × 0.006165 kg/m, and 1 ÷ 162.2 = 0.006165. Total weight = weight per meter × length of each bar × number of bars.
Imperial bar numbers are the nominal diameter in eighths of an inch, so #4 is 4/8 = 0.5 in = 12.7 mm. The calculator converts the bar number to millimeters and then uses the same d² ÷ 162 formula.
Worked example
A 12 mm bar weighs 12² ÷ 162 = 144 ÷ 162 = 0.889 kg per meter. Ten bars of 6 m each are 60 m of steel, which weighs 60 × 0.889 = 53.33 kg. Imperial: a #4 bar is 12.7 mm, so it weighs 12.7² ÷ 162 = 0.996 kg/m, or 0.669 lb/ft.
Typical weights per meter
| Metric bar | kg per meter |
|---|---|
| 8 mm | 0.395 |
| 10 mm | 0.617 |
| 12 mm | 0.889 |
| 16 mm | 1.580 |
| 20 mm | 2.469 |
| 25 mm | 3.858 |
Limits
- d² ÷ 162 is a calculated weight for a plain round bar. Deformed (ribbed) bars, mill tolerances and standard tables differ from it slightly. Where an order or a design needs the exact figure, use the weight in the product standard.
- The imperial figures use the nominal diameter, so they can differ slightly from the weights tabulated in standards for the same bar.
- The extra percentage is yours to choose. Laps, hooks, bends and cutting waste depend on the detailing, and this calculator does not work them out.
- It covers a single bar size at a time. Add up different sizes separately.
- Changing the bar-size system resets the size list, so pick the size again.
More worked examples
Ten 16 mm bars, 12 m each, with 8% extra for laps and waste: a 16 mm bar weighs 16² ÷ 162 = 1.580 kg/m, the total length becomes 10 × 12 × 1.08 = 129.60 m, and the weight is 204.80 kg (451.51 lb), shown as 0.2048 t.
Imperial: twenty-five #5 bars of 20 ft each. A #5 bar is 5/8 in, or 15.88 mm, so it weighs 1.556 kg/m (1.045 lb/ft). The total length is 500 ft (152.40 m) and the weight is 237.08 kg (522.67 lb).
A larger order: 100 bars of 12 mm × 12 m come to 1,200 m and 1,066.67 kg, or 1.0667 t.
Weights for the other metric sizes
| Metric bar | kg per meter |
|---|---|
| 6 mm | 0.222 |
| 14 mm | 1.210 |
| 18 mm | 2.000 |
| 22 mm | 2.988 |
| 28 mm | 4.840 |
| 32 mm | 6.321 |
| 36 mm | 8.000 |
| 40 mm | 9.877 |
Imperial bar numbers
| Bar | Diameter (mm) | kg per meter |
|---|---|---|
| #3 | 9.52 | 0.560 |
| #4 | 12.70 | 0.996 |
| #5 | 15.88 | 1.556 |
| #6 | 19.05 | 2.240 |
| #7 | 22.22 | 3.049 |
| #8 | 25.40 | 3.982 |
| #9 | 28.57 | 5.040 |
| #10 | 31.75 | 6.223 |
| #11 | 34.92 | 7.529 |
| #14 | 44.45 | 12.196 |
| #18 | 57.15 | 20.161 |
What the tool accepts
- The number of bars must be a whole number of at least 1. 2.5 or 0 bars shows "Please enter valid, positive values (the number of bars must be a whole number)." Leaving it blank counts as 1.
- The length must be above zero. A blank length shows "Please fill in the length of each bar." The extra percentage can be 0 or more, and blank counts as 0.
- Imperial lengths are in feet and metric lengths in meters. The total length and weight are shown in both systems.
Frequently asked questions
Where does d² ÷ 162 come from?
Steel weighs about 7,850 kg per cubic meter. The cross-section of a round bar is π ÷ 4 × d², and multiplying by the density gives about d² × 0.006165 kg per meter, which is d² ÷ 162.2. The rule rounds the divisor to 162.
What does the number in a #4 or #5 bar mean?
It is the nominal diameter in eighths of an inch, so #4 is 1/2 in and #5 is 5/8 in. The calculator also shows the diameter in millimeters.
Does it include the weight of stirrups or bends?
Only if you include their length. Enter the cut length of the bar before bending as the length of each bar; a bent bar weighs the same as the straight length it was cut from.
Can I get the number of bars from a total weight?
Not directly, but you can divide the weight by the weight of one bar, which is the weight per meter times the bar length.
How many 12 mm, 12 m bars make a tonne?
One bar weighs 12² ÷ 162 × 12 = 10.667 kg, so a tonne is 1,000 ÷ 10.667 = 93.75 bars. Bar counts must be whole numbers, so 94 bars is slightly more than a tonne.
What does the extra percentage change?
It multiplies the total length by 1 + extra ÷ 100 before the weight is worked out. With 8% extra, 120 m of bar becomes 129.60 m.
Why do I have to choose the bar size from a list?
The size menu holds the metric sizes from 6 to 40 mm and the imperial bar numbers #3 to #18. A size outside the list, such as 13 mm, is not accepted and shows "Please choose a bar size."