Concrete Calculator

How to measure

1. Measure the exact slab or pad length and width across the formwork.
2. Measure slab depth / thickness accurately (e.g., 10 cm / 4 inches for sidewalks; 15 cm / 6 inches for driveways).
3. Confirm sub-base is compacted and level to prevent hidden thickness variations.
4. Add an appropriate spillage and excavation variance waste allowance (typically 10%).

Input guide

• Enter length and width in meters or feet.
• Input slab depth in centimeters (metric) or inches (imperial).
• Apply a 10% waste margin for uneven subgrades and formwork deflection.
• Enter price per cubic meter or cubic yard to calculate total concrete cost.

Formula

The calculator converts depth into matching dimensional units (meters or feet).

It calculates three-dimensional volumetric space and adds the settling and spillage allowance.

Outputs return cubic meters (m³) for metric or cubic yards (yd³) for imperial projects.

Worked example: Residential backyard patio concrete slab

1. A patio slab measuring 5.0 m length by 4.0 m width equals 20.0 m² of surface area.
2. At a standard depth of 10 cm (0.10 m), base volume equals 2.0 m³.
3. Adding a 10% allowance for subgrade variance yields 2.20 m³.
4. The order quantity is 2.20 m³ of ready-mix concrete.

At 110 USD per cubic meter, the estimated ready-mix concrete cost is 242 USD.

Buying advice

• Confirm ready-mix truck access, chute reach, and concrete pump requirements prior to delivery day.
• Check supplier minimum load fees (many ready-mix companies charge extra for deliveries under 3–4 m³).
• Prepare curing blankets or curing compound to prevent rapid surface drying and plastic shrinkage cracks.

Common mistakes

• Entering depth as a whole meter or foot instead of converting centimeters or inches.
• Underestimating concrete consumption caused by soft, uncompacted subsoil.
• Failing to install expansion joint filler against existing building walls.
• Not accounting for thickened edges or footing trenches.