Guide
Bar sizes and the standards behind them
Rebar weight follows from a bar's nominal size and the product standard it is made to, and the markets we cover use different systems. In the US, bars are numbered #3 to #18 under ASTM A615. Up to #8 the number is the nominal diameter in eighths of an inch, so #4 is 0.500 in, and the nominal weight per foot is taken from the standard's table rather than from a formula.
In the UK, bars are specified to BS 4449 by diameter in millimeters, and product standards such as EN 10080 derive the nominal mass from the nominal cross-section and a steel density of 7,850 kg/m³. In Australia, reinforcement is often called reo, and drawings mark bars as N12, N16, N20 and so on; use the metric row of the same diameter. We do not cover Canadian bar designations here.
Actual bars can differ from the nominal mass within the tolerance of their standard; we do not quote tolerance figures. For ordering and checking deliveries, rely on the supplier's certificate or weighbridge ticket, and use the calculator to check that the order is in the right range.
Welded mesh sheets are not in this version. Their weights will be added once we have checked a source for them; until then, take the mass per sheet or per square meter from your supplier.
How to build a bar list
Work from the bending schedule or the drawings. Give each bar mark one line: its diameter or bar size, the number of bars and the cut length of one bar. Shape codes and bend details stay on the schedule; for weight, only the cut length matters.
Enter lengths with their unit. Metric schedules often give cut lengths in millimeters, and the calculator converts 2400 mm to 2.4 m for you; imperial lists in feet and inches are converted the same way.
Add an allowance for laps and waste only if the cut lengths do not already include them. If your schedule shows laps as separate bars, they are already in the count.
Check the totals by size against the delivery. The calculator groups bars of the same size, so you can compare, for example, 144 m of 12 mm bar with the line on the delivery note.
For a quick estimate before the schedule exists, enter the main bars of each element with an approximate count and length, and keep the allowance separate so you can replace the estimate with the scheduled figures later. Results are shown in pounds, kilograms and metric tons side by side, so the same list works with a US supplier and a metric one.
Export the list to Excel or PDF if you want to keep it with the schedule.
Formula, chart values and common mistakes
A metric bar's mass per meter is its cross-section times the steel density: π / 4 × d² × 7,850 kg/m³. With d in millimeters this simplifies to about d² / 162.2, so a 12 mm bar weighs 144 / 162.2 = 0.888 kg/m. US bar sizes use the published table instead: #4 weighs 0.668 lb/ft.
The US table and a cross-section formula do not match exactly, because the table values are rounded nominal weights. For #10 the formula gives about 4.31 lb/ft against 4.303 lb/ft in the table; the calculator uses the table.
- Measuring the outside diameter over the ribs: always use the nominal size.
- Mixing kg/m and lb/ft: 1 lb/ft is 1.488164 kg/m.
- Adding a lap percentage on top of laps already in the schedule: the steel is counted twice.
- Treating the result as a delivery weight: actual bars vary within the tolerance of their standard.
- Unusual diameters: the calculator still computes them by formula and warns that the size is outside the 6 to 40 mm chart.
Questions about rebar weight
How do you calculate rebar weight?
For a metric bar, square the diameter in millimeters and divide by 162.2 to get kilograms per meter, then multiply by the total length. For US bar sizes, take the weight per foot from the ASTM A615 table and multiply by the total length in feet. Add an allowance for laps and waste only if the cut lengths leave them out.
How much does #4 rebar weigh per foot?
#4 rebar weighs 0.668 lb per foot, or 0.994 kg per meter. It has a nominal diameter of 0.500 in and an area of 0.20 in². So 600 ft of #4, for example 30 bars of 20 ft, weighs 400.80 lb. For comparison, #3 weighs 0.376 lb/ft and #5 weighs 1.043 lb/ft.
How much does 12 mm rebar weigh per meter?
A 12 mm bar weighs 0.888 kg per meter: its cross-section is π / 4 × 12² = 113.1 mm², multiplied by 7,850 kg/m³. That is about 0.597 lb per foot. A 6 m bar therefore weighs 5.33 kg, and the 144 m of 12 mm bar in the worked example weighs 127.85 kg.
Why does the US chart not match the formula?
The ASTM A615 values are nominal weights published in a table and rounded, so a cross-section formula gives slightly different results for some sizes; for #10 the difference is about 0.2 %. The calculator uses the table for US bar sizes and the formula for metric bars, so each follows the way that system is specified.
Does the calculator include welded mesh?
Not yet. Mesh sheet weights will be added once we have checked a source for them, and we do not publish figures we have not checked. For now, take the mass per sheet or per square meter from your supplier and add it to the bar list total yourself, keeping the mesh on a separate line of your order.