Concrete and steel
Reinforcing steel calculator
This calculator does two jobs. For reinforcing bars, enter the size and the total length you need and it gives the weight in kilograms and how many stock lengths to buy, allowing for laps where bars join. For mesh, enter the slab area and it gives the number of sheets once the overlaps are taken off.
What you need
This calculator works out the figures in your browser, which needs JavaScript switched on. The method below shows how to work it out by hand.
Estimates for planning and budgeting. Real quantities depend on the site and the workmanship, so check with your builder before you order.
Bars are named by their diameter: Y for high-yield deformed bar (Y10, Y12, Y16) and R for round mild steel, used mostly for stirrups (R8). Their weight follows a simple rule, the diameter squared divided by 162 kilograms per metre, which is why a Y16 bar weighs more than twice a Y10.
Steel is structural. The bar sizes, spacings and laps for any slab, beam or column should come from an engineer's drawings; this calculator is for turning those drawings into an order, and for checking a supplier's quote.
How it is worked out
- Mass per metre = diameter² ÷ 162 (kg/m). A Y12 bar weighs about 0.89 kg per metre.
- Where one bar is longer than the stock length, a lap of the chosen number of diameters is added at each joint.
- Stock lengths = total length ÷ stock length, rounded up, plus the offcut allowance.
- Mesh sheets cover their size less the overlap on each side, and the count is rounded up.
What it assumes
- Bending, cutting and binding wire are not included.
- Mesh masses are typical values for the reference; check your supplier.
Common questions
How heavy is a Y12 bar?
About 0.89 kg per metre, so a 6 m bar weighs about 5.3 kg and a 12 m bar about 10.7 kg.
How many tonnes of steel does a house need?
It depends entirely on the structure. Count it from the engineer's bending schedule; this calculator turns that schedule into weights and stock lengths.
What is mesh ref 193?
A welded steel fabric for slabs and surface beds whose number is roughly its steel area in mm² per metre. Higher numbers are heavier and stronger.
Want exact quantities for your plan?
A calculator works one wall or one slab at a time. A bill of quantities works from your actual drawings and counts everything, which is what builders price against and what stops you buying twice.