Whether you’re pouring a driveway, a house slab, or a retaining wall, choosing the right rebar size is one of the most important decisions you’ll make. Get it wrong and you risk cracking, structural failure, or a failed building inspection. This guide breaks it down simply.

What Is Rebar and Why Does It Matter?

Rebar (short for reinforcing bar) is steel rod embedded in concrete to add tensile strength. Concrete handles compression well on its own — but it cracks easily under tension. Rebar prevents that. Without it, most concrete structures would fail within years.

Common Rebar Sizes and Their Uses

Size	Diameter	Typical Use
Y10	10mm	Light slabs, footpaths, garden walls
Y12	12mm	House floor slabs, driveways, light columns
Y16	16mm	Structural beams, heavy floor slabs, ground beams
Y20	20mm	Columns, retaining walls, bridge decks
Y25	25mm	Heavy structural elements, industrial floors

Which Size for a House Slab in South Africa?

For a standard residential house slab in South Africa, the most common specification is Y12 rebar at 200mm centres in both directions (a grid pattern). This is the minimum most structural engineers specify for a conventional brick-and-mortar home on stable ground.

If you’re on expansive clay soil (common in Gauteng and the Highveld), your engineer may upgrade to Y16 at 150mm centres to handle the ground movement.

How Much Rebar Do You Need?

A quick rule of thumb for a basic grid layout:

• Measure your slab length and width in metres
• Divide each dimension by your spacing (e.g. 0.2m for 200mm centres)
• Add 1 to get the number of bars per direction
• Multiply by the slab dimension in the other direction for total metres of bar
• Double it (for the grid — bars run both ways)

Example: A 10m × 10m slab at Y12, 200mm centres needs roughly 1,000 metres of rebar (about 166 bars at 6m lengths).

Always Check with Your Structural Engineer

South African building regulations (SANS 10400) require structural drawings approved by a registered engineer for most buildings. The sizes above are general guidelines — your engineer’s spec sheet is the final word.

Buy Rebar Online — Delivered Nationwide

Indus Alloy supplies Y10, Y12, Y16, Y20, and Y25 rebar in standard 6-metre lengths, cut lengths, and bulk quantities. We deliver nationwide across South Africa with competitive transport rates. All our rebar is SANS-certified.

Browse our rebar range → or WhatsApp us on 061 308 7652 for a bulk quote.