zacdaddytools
Estimate concrete volume, litres, weight, bag quantities and cost for slabs, footings, round bases and post holes.
Measurements and calculations stay in your browser.
Quick depth
Choose a depth from your plans or specification; these are quick entries, not structural advice.
Optional extra for measurement variation, uneven excavation or spillage.
Enter the dimensions of a slab, footing, round base or post holes to estimate the concrete volume you need. The calculator converts every measurement to metres before calculating volume, then shows both cubic metres and litres.
You can mix metric and imperial measurements. For example, a length in feet, width in feet and depth in millimetres can be used together without manually converting them first. One cubic metre equals 1,000 litres.
The exact volume is the result of the entered dimensions. The optional extra allowance produces a separate order quantity that can help account for measurement variation, uneven excavation, spillage and similar practical factors.
An allowance is not mandatory and does not replace accurate measurement. Check supplier ordering requirements and your project specification before ordering.
3 m × 2 m × 100 mm = 0.600 m³ of concrete.
With a 10% allowance: 0.600 × 1.10 = 0.660 m³.
For a footing or trench, the calculator multiplies length × width × depth × the number of identical sections. Round bases, columns and post holes use the cylinder formula: π × radius² × height × quantity.
For example, 12 post holes with a 150 mm diameter and 600 mm depth require approximately 0.127 m³ before any allowance. A footing 10 m long, 300 mm wide and 300 mm deep requires 0.900 m³ for one section.
Diameter: 150 mm. Depth: 600 mm. Number of holes: 12.
π × (0.075 m)² × 0.600 m × 12 ≈ 0.127 m³.
Bag yields vary between products, so enter the litres-per-bag yield printed by the manufacturer. The calculator always rounds the number of bags up to a whole bag. Bag weight alone is not used as a substitute for the manufacturer’s stated yield.
The approximate weight uses a typical normal-concrete density of 2,400 kg per cubic metre. Actual density varies with mix and aggregate, so this is a planning estimate rather than an engineering value.
This calculator estimates concrete quantities from the dimensions you enter. Structural requirements, concrete grade, reinforcement and minimum thickness depend on the project. For structural work, follow your plans or specification or seek appropriate professional advice.
FAQs
Choose the shape that matches your job, enter each measurement and use the displayed cubic-metre and litre estimate. Add an optional allowance if appropriate for the project.
For a rectangular slab, multiply length × width × depth after converting each measurement to metres. Cylindrical holes and columns use π × radius² × depth.
One cubic metre equals 1,000 litres.
The appropriate allowance depends on how accurately the excavation and measurements can be controlled. The calculator offers 0%, 5%, 10% and 15% options but does not make any allowance mandatory.
Use Slab / Base, then enter the planned length, width and depth. For example, 3 m × 2 m × 100 mm equals 0.600 m³ before allowance.
Use Post Holes, enter the hole diameter, depth and number of holes. The calculator uses the cylindrical volume formula for all identical holes.
Enter the manufacturer’s stated yield in litres per bag. The calculator divides the required litres by that yield and rounds up to the next whole bag.
Different products, mixes and stated yields vary by manufacturer. Use the yield printed on the bag rather than assuming a universal yield from bag weight.
Yes. Each dimension has its own unit selector, so metric, imperial and mixed measurements are converted centrally before calculation.
Required thickness depends on the project, loads, ground conditions, reinforcement and specification. This calculator does not prescribe structural thicknesses.