Concrete Calculator
Calculate concrete volume needed for slabs, footings, columns.
┌────────── L ──────────┐
│ │ W
└───────────────────────┘
depth (D)Frequently Asked Questions
How do I calculate how much concrete I need?
For a slab: Length × Width × Thickness (all in metres) = cubic metres. A 4m × 3m slab at 100mm (0.1m) thick = 1.2 m³. Always add 10% for waste and spillage. In imperial: Length (ft) × Width (ft) × Thickness (ft) ÷ 27 = cubic yards.
How many bags of concrete mix make a cubic metre?
Approximately 108 bags of 20kg premix concrete make 1 m³ (at standard mix ratio). For 25kg bags: ~86 bags. For small pours, bagged premix is convenient. For pours over 1 m³, ordering ready-mix concrete delivered by truck is more economical and practical.
What thickness should a concrete slab be?
Residential footpaths and patios: 75–100mm (3–4 inches). Driveways for passenger vehicles: 100–125mm (4–5 inches). Driveways for trucks: 150mm+ (6+ inches). Garage floors: 100–125mm. Floor slabs with reinforcement: 100–150mm. Always check local building codes.