Rebar Calculator
Calculate the number of bars, total length and steel weight required for a reinforcement grid, by bar diameter and spacing.
Rebar Calculator
Calculate bar quantity, length and weight for a reinforcement grid.
Calculating Rebar Quantity And Weight
Reinforcing bar (rebar) is laid in a grid pattern in both directions across a reinforced element. For a rectangular grid, the number of bars running in each direction is ceiling(cross dimension ÷ spacing) + 1, and total bar length is the sum of each direction's bar count multiplied by the length it spans.
Bar weight is calculated directly from its physical properties: mass per metre = π × (diameter ÷ 2)² × 7,850 kg/m³, using standard steel density. This is the same formula used to derive the published mass-per-metre figures for standard deformed bar sizes (N10 through N24), so the result reflects genuine bar weight for whichever diameter you select, rather than a rounded lookup value.
What Information You Need To Enter
Enter the length and width of your reinforcement grid in metres, select a bar spacing (100 mm to 300 mm centres), and select a bar diameter from N10 to N24.
Understanding Your Results
You will see the total number of bars required, the combined bar length, the mass per metre for your selected diameter, and the total steel weight. Actual reinforcement layout, including any additional trimmer bars or laps at splices, should always follow your engineering drawings.
Why Accurate Estimating Matters
Steel reinforcement is priced by weight, so an accurate estimate helps you budget correctly and order the right quantity of bar for your project ahead of a formal engineering take-off.
Frequently Asked Questions
What does N12, N16 or N20 mean?
The "N" denotes a standard deformed (ribbed) reinforcing bar under Australian standards, and the number is the nominal bar diameter in millimetres -- N12 is a 12 mm diameter bar, N16 is 16 mm, and so on.
How is bar weight calculated?
Bar weight per metre is calculated from its cross-sectional area (based on diameter) multiplied by the density of steel, approximately 7,850 kilograms per cubic metre. This calculator computes this directly rather than relying on a rounded reference table.
Does bar spacing affect strength?
Yes -- closer spacing generally provides more reinforcement per square metre and is specified where higher structural strength is required. Spacing is determined by your structural engineer based on the loads involved.
Does this include laps or splices?
No -- this calculator estimates a basic grid based on your entered dimensions. Additional bar length for laps at splices, starter bars, or trimming around penetrations should be added according to your engineering drawings.
Where is rebar used in residential construction?
Common applications include reinforced slabs, footings, retaining walls and structural beams. Lighter applications like standard driveways typically use mesh instead -- see our Reinforcement Mesh Calculator.
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Need An Exact Price, Not Just An Estimate?
The Rebar Calculator gives you a fast, useful planning figure. For a fixed, accurate price backed by a site assessment, request a free professional quotation from HPL Construction.
