Start typing to discover tools…
 View all results
Construction and Home

Rebar Calculator

Estimate reinforcing-bar quantity, spacing, total cut length, stock bars, steel weight, waste, and optional cost for slab grids, reinforced walls, beams with stirrups, or a custom group of bars.

Reinforcement Details

Select the project type, measurement system, and bar size.

Enter length in metres.
Enter width in metres.
Bars run along the slab length; spacing is in millimetres.
Bars run along the slab width; spacing is in millimetres.
Enter concrete cover in millimetres.
Use 2 when calculating matching top and bottom grids.
Enter supplier stock length in metres.
Use an allowance suitable for laps, hooks, cuts, and offcuts.
Optional steel cost per kilogram.

Your reinforcement estimate will appear here

Enter the dimensions, spacing, bar size, and waste allowance, then calculate the reinforcement.

Estimated reinforcing-steel weight
—
Including the selected waste and lap allowance
Base cut length —
Length with waste —
Stock bars required —
Bar placements —
Selected bar size
—
Weight per unit length
—
Waste and lap allowance
—
Selected stock length
—

Calculation breakdown

Estimated reinforcing-steel cost —
This is a quantity-planning estimate, not a reinforcement design or bar-bending schedule. Bar size, spacing, cover, anchorage, development length, hooks, laps, couplers, curtailment, seismic detailing, and placement must follow the approved structural drawings and applicable code.

What Does the Rebar Calculator Estimate?

The calculator converts slab, wall, beam, or custom-bar details into an estimated bar count, cut length, stock-bar quantity, and steel weight. An optional unit price can be used for a material-cost estimate.

Included estimates

  • Bars in each slab or wall direction
  • Longitudinal bars and beam stirrups
  • Total base cut length
  • Length after waste and lap allowance
  • Stock reinforcing bars to purchase
  • Steel weight using the selected diameter
  • Optional cost per kilogram or pound

How Is Rebar Weight Calculated?

Steel weight is calculated from the cross-sectional area of the selected bar and a steel density of approximately 7,850 kilograms per cubic metre. The result is multiplied by total bar length.

Planning considerations

  • Stock lengths vary by supplier and region
  • Laps may be longer than a general waste allowance
  • Hooks and anchorage can add significant length
  • Separate bar sizes may be used for main bars and stirrups
  • Offcuts may or may not be reusable elsewhere
  • A structural bar schedule should control final ordering

How to Use the Rebar Calculator

1

Select metric or imperial units

Choose the unit system used on the drawings and select the required metric diameter or US rebar designation.

2

Choose the reinforcement type

Calculate a slab grid, wall grid, beam with stirrups, or a known quantity of custom-length bars.

3

Enter dimensions, cover, and spacing

Use the structural drawings for dimensions, clear cover, number of layers or faces, and centre-to-centre spacing.

4

Add waste and stock length

Enter the available supplier bar length and an allowance for laps, hooks, cuts, damage, and unusable offcuts.

5

Review quantity, weight, and cost

Use the result as a preliminary ordering guide and verify it against the approved bar-bending schedule.

Common Rebar Sizes and Approximate Weight

Metric diameter Approx. kg/m Comparable US size Approx. lb/ft
10 mm 0.617 kg/m #3 — 9.525 mm 0.376 lb/ft
12 mm 0.888 kg/m #4 — 12.7 mm 0.668 lb/ft
16 mm 1.578 kg/m #5 — 15.875 mm 1.043 lb/ft
20 mm 2.466 kg/m #6 — 19.05 mm 1.502 lb/ft
25 mm 3.853 kg/m #8 — 25.4 mm 2.670 lb/ft
32 mm 6.313 kg/m #10 — 32.26 mm 4.303 lb/ft

Rebar Calculation Formulas

Number of bars at maximum spacing

Bar count equals ceiling(effective dimension ÷ spacing) + 1. The effective dimension is the overall dimension minus cover at both edges.

Grid reinforcement length

Total grid length equals bars in direction one × cut length one + bars in direction two × cut length two, multiplied by the number of layers or reinforced faces.

Beam stirrup length

Approximate stirrup length equals the inner rectangular perimeter plus a hook allowance. This calculator uses a general hook allowance equal to 24 bar diameters for estimating.

Rebar weight

Weight equals steel cross-sectional area × steel density × total length. A density of approximately 7,850 kg/m³ is used.

Frequently Asked Questions

The quantity depends on slab length, width, edge cover, spacing in both directions, and the number of reinforcement layers. The calculator determines the bar count and cut length for each direction.

It includes only the percentage entered as waste and laps. Required lap length depends on bar size, concrete strength, cover, confinement, bar location, and structural code requirements.

Total reinforcement length after the waste allowance is divided by the selected stock-bar length and rounded up. Actual cutting optimisation can require additional bars.

This version applies one selected size to the complete beam estimate. When main bars and stirrups use different sizes, calculate each group separately using custom-bar mode for a more accurate weight.

Yes. Reinforcement spacing on structural drawings is normally specified centre to centre. Always follow the notation and details shown on the approved drawings.

No. It is a preliminary quantity calculator. Final fabrication and ordering should use the approved bar-bending schedule, structural drawings, revisions, and project specifications.