🧱 Concrete Mix Calculator
Describe your slabs, footings or posts: get the concrete volume and the cement, sand, gravel and water quantities, in bags, buckets and wheelbarrows.
⚠️ Indicative mixes for ordinary DIY work. This is not a structural calculation: for load-bearing work (house foundations, suspended slabs, retaining walls…), follow an engineer’s design or a professional’s specification and local building codes.
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About the Concrete Mix Calculator
Before ordering materials or starting the mixer, you need to know how much concrete to pour and how many bags of cement, and how much sand and gravel, to buy. This calculator adds up your elements (slab, strip footing, pad, round post) and applies the mix for the selected use, with a waste margin.
How to Use the Calculator
- Add your elements: type, dimensions (lengths in m or cm, thickness in cm) and quantity, for example 6 identical pads.
- Pick the use: blinding, footings, general purpose, reinforced concrete or mortar.
- Set the bag size (25 or 35 kg), the waste (5% by default), the bucket and the wheelbarrow.
- Read the result in kg, litres, buckets and wheelbarrows, with the batch for one bag of cement, then copy it.
Mixes Explained
- General purpose concrete at 350 kg/m³: 350 kg of cement, 500 L of 0/4 sand, 800 L of 4/20 gravel and about 175 L of water per m³. For one 35 kg bag: 5 buckets of sand, 8 buckets of gravel and about 17 L of water.
- Blinding concrete: lean (150 to 250 kg/m³), only used to cover the bottom of the trench and keep the reinforcement clean.
- Unreinforced footings: about 300 kg/m³; as soon as there is reinforcement, use 350 kg/m³.
- Highly loaded reinforced concrete: columns, lintels: about 400 kg/m³.
- General mortar: 350 kg of cement per m³ of sand (10 buckets of sand per 35 kg bag), no gravel.
- Volumes: slab = length × width × thickness; round post = π × radius² × height. Sand and gravel are counted loose, at about 1.6 and 1.5 kg/L.
Tips
- All-in ballast (0/20): if you buy a ready sand-gravel mix, count about 10 buckets of mix per 35 kg bag at 350 kg/m³.
- Always use the same bucket, filled level without packing, to keep the mix consistent.
- Above roughly 1 m³, compare with ready-mix concrete delivered by truck: it is often easier and more consistent.
- Protect fresh concrete from sun, wind and frost, and keep it damp for the first days.
Common Mistakes and Limits
- Too much water: a runny mix is easier to pour but much weaker.
- Damp sand: it bulks up and already contains water; adjust the water accordingly.
- Thickness unit: a 10 cm slab is 0.1 m³ per m², not 1 m³.
- Not a structural design: reinforcement, thickness and concrete class of load-bearing work are a professional’s job.
Privacy & Security
- 100% in your browser: no data is sent to a server.
- No sign-up: free and instant.
- Works offline once the page has loaded.