Bar weights and quantities
Bars per m² and steel weight per m² of a two-way mat
- where
- metres of bar per m² in each direction (m/m²)
- bar spacing in each direction (mm)
- bar length per m² for all mats (m/m²)
- number of identical mats
- steel mass per m² (kg/m²)
- bar diameter in each direction (mm)
- bar crossings per m² in each mat
Explain this equation
Gives the metres of bar and kilograms of steel in each square metre of a two-way mat. Use it for quick take-offs, rates per m², or comparing loose bars with mesh.
lx and ly are the metres of bar per m² in each direction: bars at 200 mm centres put five metres of bar in every square metre. dx and dy are the bar sizes, k the number of identical mats, and ni the number of crossings to tie in each mat.
Each direction contributes its length per m² times its mass per metre, d²/162, so the steel weight is the sum of the two directions, multiplied by the number of mats. Crossings per m² are simply the bars per metre each way multiplied together.
Sense check: 10 mm at 200 mm both ways gives 6.17 kg/m², the same as A393 mesh. 12 mm at 200 mm both ways is about 8.9 kg/m² per mat.
Watch out: laps, edge bars and trimmers are extra and can add 10 to 15 per cent on a real slab.
Turns bar size and spacing into metres of bar and kilograms of steel per square metre of slab or wall, for quick take-offs and comparing loose bar against mesh.
Enter your values to see the result.
Good to know
Bars at s mm centres give 1000/s metres of bar in every square metre in that direction. Multiply by the mass per metre and add the other direction. Laps, edge bars, trimmers and chairs are extra: on a typical slab they can add 10–15% to the plain mat weight. As a check, 10 mm bars at 200 mm both ways give 6.17 kg/m², the same as A393 mesh (6.16 kg/m²).
Common mistake
Counting only one direction, or forgetting the second mat in a top-and-bottom slab.
Limits
Plain rectangular mat with no laps or edge effects. Use the bar count and schedule calculators for the exact quantity.
Sources
- BS 4449:2005+A3:2016 Steel for the reinforcement of concrete. Weldable reinforcing steel. Bar, coil and decoiled product
- BS 4483:2005 Steel fabric for the reinforcement of concrete. Specification
- CR Steel, Steel calculator sheet (bar mass per metre, metres per tonne, 12 m bars per tonne; BS 4483 mesh masses: A142 2.22, A193 3.02, A252 3.95, A393 6.16 kg/m²)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Always work to the engineer’s drawings and bending schedules, BS 8666, BS EN 1992, BS EN 1090-2, BS 5531/the BCSA National Structural Steelwork Specification and manufacturers’ data. Lifting must be planned under LOLER by a competent person.