Rebar
Calculate reinforcement for concrete elements
How the calculation works
Add an element (slab, foundation slab, beam, column), enter dimensions, bar spacing and diameter, and a waste percentage. The calculator works out length, mass and the number of 6 m bars, and for meshes the number of sheets.
Formula and assumptions
For a slab with bars in two directions: bars = ⌈dimension ÷ spacing⌉ + 1, length = bars × span. Total × (1 + waste). Mass = length × kg/m of bar (e.g. Ø8 = 0.395 kg/m). 6 m bars = ⌈length ÷ 6⌉. For meshes: sheets = ⌈area ÷ effective sheet area × (1 + waste)⌉ × layers. The kg/m values come from the table in the app.
Worked example
Slab 4 × 5 m, Ø8 at 20 cm both ways, 1 layer, 5 % waste: along the 5 m direction ⌈4 ÷ 0.2⌉ + 1 = 21 bars = 105 m; along the 4 m direction ⌈5 ÷ 0.2⌉ + 1 = 26 bars = 104 m. Total 209 m × 1.05 = 219.45 m. Mass 219.45 × 0.395 = 86.7 kg. 6 m bars: 219.45 ÷ 6 = 36.6 → 37.
What affects real consumption
- Laps, hooks and anchorage are not included unless you add them through the waste percentage.
- Concrete cover and spacing according to the design.
- Actual mass differs between ribbed and plain bar.
Frequently asked questions
Does the calculation include bar laps?
Laps are not counted separately; account for them through the waste percentage or according to the reinforcement design.
Is the result a structural calculation?
No – the calculator only quantifies the layout you enter; the amount and layout of reinforcement is set by the structural design.