Steel Rebar Calculator
Find the total weight of rebar and how many rods you need for a slab or column.
Enter your numbers
Example: 100
Example: 125
Example: 1
Example: 12
Example: 12
Recent
Formula
How the calculation works
The concrete volume is the slab area times its thickness, and multiplying by the steel percentage and the density of steel gives the weight.
The weight per foot of a rod is its diameter squared divided by 162, a standard site formula for rebar.
Dividing the total weight by the weight of one rod gives the number of rods, rounded up to whole bars.
Common mistakes
- Using the slab thickness in millimetres without dividing by a thousand, which inflates the steel weight enormously.
- Assuming a steel percentage without an engineer's input: slabs, beams and columns each need different ratios.
When to use it
- Use it to estimate rebar weight and rod count before ordering steel.
- It is not a structural design; the steel ratio must come from a qualified engineer.
Worked example
A 100 sq ft slab 125 mm thick at 1% steel with 12 mm rods needs about 981.25 kg of steel, which is 92 rods of 12 ft.
Common questions
What percentage of steel is normal for a slab?
About 0.8 to 1.2 percent of the concrete volume for a typical residential slab.
How much does a 12 mm rod weigh per foot?
A 12 mm rod weighs about 0.888 kg per foot using diameter squared divided by 162.
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