Getting an accurate reinforcement quantity isn’t a case of measuring the slab and applying a rule of thumb — it depends on the design, the layout, and how the reinforcement is detailed. This guide covers what actually drives the number, not a shortcut to skip proper detailing.

For mesh

Mesh quantity comes down to the area to be covered, the standard sheet size for the mesh code specified (commonly 3.6m × 2.0m or 4.8m × 2.4m), and the lap required between adjacent sheets — typically at least one full mesh square, per the relevant standard or your engineer’s specification. Overlapping sheets means the area of mesh you buy is always somewhat more than the raw slab area, and the exact laps depend on the mesh type and the design.

For rebar

Rebar quantity comes from the bar bending schedule — the total number of bars of each shape and size, their individual cut lengths, and the required lap lengths where bars are spliced together (lap length depends on bar diameter, concrete grade and whether the bar is in tension or compression — see our guide to lapping and cover). Without a schedule, an estimate can be built from the structural drawings, but it’s genuinely an estimate, not a precise figure.

Converting to weight

Once you know the lengths and diameters, weight follows from the standard mass-per-metre for each bar size (heavier for larger diameters) or weight-per-square-metre for each mesh code — figures you’ll find on each size’s own specification page. Weight is what drives cost and delivery planning, so it’s worth getting this right rather than rounding generously and over-ordering.

The most reliable way to get a number

If you have a structural drawing or a bar bending schedule, send it to us and we’ll put together an accurate quote against it — far more reliable than any online calculator, because it accounts for your actual layout, laps and wastage. Call 0207 856 0141 or use our contact form and attach what you’ve got.

This guide is intended as general background only. The reinforcement your project actually needs — bar size, mesh type, cover, spacing, lap lengths — is set by your structural engineer’s drawings or your building control surveyor, not by a website. Always work to the specification you’ve been given, and if you don’t have one, ask your engineer before you order.

Need reinforcement for your project? Get a fast, competitive quote or call 0207 856 0141 — we deliver rebar and mesh across London and the South East.