Calculate how much concrete you need for slabs, columns, and footings. Shows cubic meters, cubic yards, and the number of 25 kg or 40 kg bags. Free and instant.
A concrete calculator determines how much concrete is needed for a slab, footing, or column based on its dimensions. It converts the volume into cubic meters or cubic yards and estimates the number of pre-mixed bags required, helping avoid over-ordering or running short on a job site.
0.9 m³
Volume (m³)
1.18 yd³
Volume (yd³)
87
25 kg Bags
44
50 kg Bags
71
60 lb Bags
53
80 lb Bags
Last updated:
Concrete
Calculating the required amount of concrete is critical for any construction project. Too little stops the job; too much is costly waste. The volume is calculated on a simple principle: for slabs and footings, it is length × width × thickness (in meters), and for a circular column, it is π × (diameter/2)² × height.
Our calculator supports both metric (cm/m³) and imperial (ft/in/yd³) systems, and automatically shows the number of bags of concrete in various sizes (25 kg, 50 kg, 60 lb, 80 lb).
Structure Types
Concrete slab — a horizontal structure: garage floors, patios, floor surfaces. Thickness is typically 10–20 cm for residential use. For heavier loads, it is reinforced with a metal mesh or rebar.
Circular column — a vertical element with a round cross-section: support pillars, fence posts. Diameter and height determine the volume using the cylinder formula. Square footing — a foundation under walls or columns: a rectangular volume with greater thickness.
Concrete Bags
For small projects, buying pre-mixed bags of concrete is more economical than ordering a truck. A 25 kg bag covers approximately 0.0104 m³, and a 50 kg bag covers about 0.0208 m³. In the American system, a 60 lb bag yields about 0.45 cubic feet (0.01274 m³), and an 80 lb bag yields about 0.60 cu ft (0.01699 m³).
For projects over 2–3 m³, ordering ready-mixed concrete by truck is more cost-effective. Always order with a 10% buffer for mixing and pouring losses.
Tips
Add a 10% buffer
Always order 5–10% more than calculated to account for mixing losses and surface irregularities.
Concrete grade
For foundations and slabs, use at minimum class C20/25. For driveways and garages, use C25/30 or higher.
Temperature matters
Do not pour concrete below 5°C or above 35°C without special measures — it will not cure properly.
Reinforcement
For slabs wider than 2 m and load-bearing structures, always reinforce with metal mesh or rebar.
Curing time
Concrete reaches 70% strength in 7 days and full strength in 28 days. Keep it moist during this period.
Ready-mix vs site-mixed
For volumes over 1 m³, ready-mix delivery is more consistent and saves significant time.
For a concrete slab, multiply length × width × thickness (all in the same unit). For example, a 3m × 3m slab at 10 cm (0.10 m) depth = 0.9 m³. Our calculator handles unit conversion automatically — enter dimensions in cm or ft/inches.
A standard 25 kg bag of concrete mix covers approximately 0.0104 m³, meaning you need about 96 bags per cubic meter. A 50 kg bag covers about 0.0208 m³ (48 bags/m³). For projects over 2 m³, ordering ready-mix concrete by truck is usually more economical.
A circular column uses the cylinder formula: π × (diameter ÷ 2)² × height. For example, a column with a 30 cm (0.3 m) diameter and 3 m height = π × 0.15² × 3 ≈ 0.212 m³.
Yes — it's recommended to add 5–10% to account for spillage, uneven surfaces, and mixing losses. If the slab area has irregular edges or the ground is not perfectly level, add 10% to be safe.
A slab is a horizontal surface (floor, patio, driveway), typically 10–20 cm thick. A footing is a structural foundation element placed under walls or columns, usually thicker (20–60 cm) and narrower, designed to transfer loads to the soil.