Concrete Calculator
Calculate concrete needed for slabs, footings, and more.
100 mm is a common slab thickness
Common for paths, pads, and light slabs
Concrete volume
1.2 m³
1.57 cubic yards
If mixing yourself
Cement
288 kg (12 × 25 kg bags)
Sharp sand
0.64 tonnes (640 kg)
Aggregate (gravel)
0.9 tonnes (900 kg)
Or buy pre-mixed bags
Approx 25 kg bags
97
Approx 20 kg bags
121
Mix quantities are dry-material estimates from the ratio you chose — water, compaction, and supplier densities will vary. Ready-mix is often better for larger pours. Add a little extra for uneven ground.
In-depth explanation
Estimate concrete volume for a rectangular slab, then see DIY mix quantities (cement, sand, and aggregate — or ballast) for common ratios, plus rough pre-mixed bag counts. Everything runs locally in your browser — your inputs are not uploaded to produce the result.
If you’re mixing yourself. A typical general mix is 1 part cement : 2 parts sharp sand : 3 parts aggregate. Choose that ratio (or another) to see estimated kilograms and tonnes. All-in ballast is sand and stone already combined. A 1:5 cement:ballast mix replaces separate sand and aggregate.
Garden paths are often ~75–100 mm; driveways thicker. Follow structural guidance for loads. They’re approximate. Ready-mix is usually better for larger pours; bags and DIY mixes vary by brand and moisture. Tweak the inputs above to compare options, then copy or note the result you need.
Volume is length × width × depth for a slab. Mix ratios (1:2:3 cement:sand:aggregate, or ballast mixes) are DIY starting points. Moisture in sand changes how a bag behaves; ready-mix is more consistent for larger pours.
Depth depends on use: a garden path is not a driveway. Reinforcement, sub-base, and falls are structural choices this page does not design. Bag counts are approximate.
Frequently asked questions
Do I need sand as well as cement?
Yes if you’re mixing yourself. A typical general mix is 1 part cement : 2 parts sharp sand : 3 parts aggregate. Choose that ratio (or another) to see estimated kilograms and tonnes.
What is ballast?
All-in ballast is sand and stone already combined. A 1:5 cement:ballast mix replaces separate sand and aggregate.
What depth should I use?
Garden paths are often ~75–100 mm; driveways thicker. Follow structural guidance for loads.
Are bag counts exact?
They’re approximate. Ready-mix is usually better for larger pours; bags and DIY mixes vary by brand and moisture.
Related tools
Explore similar utilities you might find useful next.