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Rebar for foundations: diameter, steel grade and weight
Which bars to use for strip and slab foundations, how A500C differs from A240C and how to turn metres into tonnes.
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Rebar is the skeleton of a foundation. Getting the diameter or steel grade wrong is expensive: cracks do not show up at once, but a few seasons later.
Diameter
Strip foundations of private houses usually take 10–14 mm longitudinal bars and 6–8 mm stirrups. A 200–300 mm slab takes 12–16 mm. Exact values come from a structural calculation.
Steel grade
- A500C — ribbed, weldable, the usual choice for foundations.
- A240C — plain, for stirrups and fixing elements.
Only bars with the "C" index may be welded.
Working out the weight
Rebar is sold by the tonne, but you plan it in metres. Mass of one metre:
| Diameter | kg per metre |
|---|---|
| 8 mm | 0.395 |
| 10 mm | 0.617 |
| 12 mm | 0.888 |
| 14 mm | 1.210 |
Multiply the total length by the mass per metre and add 5–7 % for laps and offcuts.
Every product in the Metal section has a calculator: enter metres to get tonnes and the truck delivery price.
A500C and A240C bars are in Rebar; box sections for frames are in Box sections.
