Rebar Weight Calculator Diameter Squared Does the Work
Pick the bar size, enter the total length, and get the weight in kilograms or pounds.
One Rule to Remember
Weight per metre in kg is roughly d² ÷ 162, with d in millimetres.
Total Length, Not Bar Count
Forty bars of 6 m is 240 m. Add laps and bend allowances before you enter the figure.
How much does rebar weigh?
At a Glance
Reinforcing bar weight is the cross-section times the length times the density of steel, 7,850 kg/m³. Because the cross-section goes with the square of the diameter, a 20 mm bar weighs four times what a 10 mm bar does, not twice. A 12 mm bar is 0.888 kg per metre; a US #4 is 0.668 lb per foot.
Two designation systems are in use, and a bar schedule uses whichever the drawing does. Under ASTM A615, bars #3 to #8 carry the diameter in eighths of an inch — #4 is ½ in — while #9 and up are tabulated sizes whose cross-sections replace the old square bars. Under EN 10080 the designation simply is the diameter in millimetres.
| Bar | Diameter | Cross-section | Weight |
|---|---|---|---|
| 8 mm | 8 mm | 50.3 mm² | 0.395 kg/m |
| 10 mm | 10 mm | 78.5 mm² | 0.617 kg/m |
| 12 mm | 12 mm | 113.1 mm² | 0.888 kg/m |
| 16 mm | 16 mm | 201.1 mm² | 1.578 kg/m |
| 20 mm | 20 mm | 314.2 mm² | 2.466 kg/m |
| 25 mm | 25 mm | 490.9 mm² | 3.853 kg/m |
| #3 | 3/8 in | 71.3 mm² | 0.376 lb/ft |
| #4 | 1/2 in | 126.7 mm² | 0.668 lb/ft |
| #5 | 5/8 in | 197.9 mm² | 1.044 lb/ft |
| #8 | 1 in | 506.7 mm² | 2.673 lb/ft |
| #11 | 1.410 in | 1,007 mm² | 5.314 lb/ft |
weight = (π/4 × diameter²) × total length × 7,850 kg/m³These are the values the calculator loads by default.
Take the cross-section
π/4 × 12² = 113.1 mm², which is 0.0001131 m².
Apply the density
0.0001131 × 7,850 = 0.888 kg per metre.
Multiply by the length
0.888 × 100 = 88.78 kg.
Check it against the shortcut
d² ÷ 162 = 144 ÷ 162 = 0.889 kg/m — the same figure to three decimals, which is why that rule survives on site without a calculator.
The number has three ordinary uses, and each one wants a slightly different reading.
Ordering. Steel is sold by weight, so this is the figure on the quote. Order by total length per size, then convert — a schedule that mixes sizes needs the calculation repeated per size and summed, because the squared relationship means you cannot average diameters.
Checking a delivery. Nominal weight and actual weight differ: ASTM A615 and EN 10080 both allow a mass tolerance, typically around ±4.5 % on small bars and ±4 % on larger ones. A load a few percent under nominal is within spec, not short.
Planning a lift. Bundles are heavy faster than they look. 240 m of 16 mm bar — forty 6 m bars — is 379 kg, and the same bundle in 25 mm is 925 kg.
For other sections, Pipe Weight Calculator handles hollow tube and Concrete Calculator covers the pour the bar goes into.
Nominal weight, plain bar
The calculation uses the nominal diameter — the diameter of a smooth bar of the same cross-section. Real reinforcing bar is ribbed, and the ribs are already accounted for in that nominal figure, which is why it is the number every standard and every mill certificate quotes.
Results for the ASTM sizes land within about 0.2 % of the published nominal weights, the difference coming from rounding in the tabulated diameters. Couplers, tie wire, spacers, chairs and galvanising are not included, and neither is scrap or offcut allowance — add those to the length before you order.