Reinforcement steel by bar diameter: 10, 12, 16 and 20 mm
Steel is the largest single cost in the frame of a building, and it is bought by weight. Knowing the weight per metre of each diameter lets you check a bar schedule or a supplier's delivery.
Weight per metre
The unit weight of a round bar in kg per metre is the diameter in mm squared divided by 162 (about). This gives:
| Diameter | kg per metre | kg per 12 m bar | Bars per tonne |
|---|---|---|---|
| 10 mm | 0.617 | 7.4 | about 135 |
| 12 mm | 0.888 | 10.7 | about 94 |
| 16 mm | 1.58 | 18.9 | about 53 |
| 20 mm | 2.47 | 29.6 | about 34 |
Where each size is used
- 10 mm: stirrups and ties in columns and beams, and slab reinforcement in light work.
- 12 mm: slab bars, secondary beam bars and stair reinforcement.
- 16 mm: main bars in beams and columns for ordinary buildings.
- 20 mm: heavily loaded columns, footings and the lower floors of taller buildings.
The final sizes and spacing always come from the structural engineer's drawings. They depend on loads, spans and the number of storeys.
Counting bars and wastage
Divide the weight needed by the weight of a 12 m bar to get the number of bars. Add wastage for cutting, laps and bending, usually 3 to 7%. Binding wire is about 1% of the steel weight.
See it for your own plan
The cost screen of the PlanCraft 3D planner splits the estimated steel for footings, columns, beams, slabs and stairs into 10, 12, 16 and 20 mm bars, with a 12 m bar count and the cost at your own price per kg.
The split in the planner is a planning estimate based on typical ratios. It is not a bar bending schedule. Use your engineer's schedule when you buy and cut steel.
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