Concrete Mix Ratio Calculator
Estimate how much cement, sharp sand, gravel and water you need for a concrete pour. Enter the width, height and depth of your slab, footing or structure in meters and get material quantities instantly.
Calculate Concrete Mix Materials by Volume
Concrete Mix Ratio Formula
Where:
- \(W\) — width of the structure (m)
- \(H\) — height of the structure (m)
- \(D\) — depth of the structure (m)
- \(V\) — total concrete volume (m³)
- \(C\) — cement required (kg)
- \(S\) — sharp sand required (kg)
- \(G\) — gravel required (kg)
- \(W_{water}\) — water required (L)
The material coefficients correspond to a general-purpose concrete mix of approximately 1 : 2 : 4 (cement : sand : gravel by mass), which is suitable for slabs, paths, footings and other non-structural or lightly loaded work.
Concrete Mix Ratio – Calculation Example
Example: a small concrete pad measuring 1 m wide, 1 m high (long) and 1 m deep, giving a volume of 1 m³.
\[ V = 1 \cdot 1 \cdot 1 = 1 \text{ m}^3 \]
\[ C = 1 \cdot 320 = 320 \text{ kg}, \quad S = 1 \cdot 600 = 600 \text{ kg}, \quad G = 1 \cdot 1200 = 1200 \text{ kg}, \quad W_{water} = 1 \cdot 176 = 176 \text{ L} \]
Result: for 1 m³ of concrete you need approximately 320 kg of cement, 600 kg of sharp sand, 1200 kg of gravel and 176 L of water.
How to use the calculator
- Measure your pour and enter the Width in meters (e.g. 2.5).
- Enter the Height in meters — for a slab this is the length of the pour.
- Enter the Depth in meters — for a slab this is the thickness (e.g. 0.1 for a 10 cm slab).
- Read the results: Volume in m³, plus Cement required (kg), Sharp Sand required (kg), Gravel required (kg) and Water required (L).
For irregular shapes, split the pour into rectangular sections, calculate each one separately and add the material quantities together.
What is a concrete mix ratio?
A concrete mix ratio defines the proportions of cement, sand, gravel and water used to make concrete. The proportions determine the strength, workability and durability of the finished mix. This calculator is based on a general-purpose mix of roughly 1 : 2 : 4 (cement : sharp sand : gravel), a widely used recipe for paths, patios, shed bases, kerbs and similar DIY and light construction work. Stronger mixes for structural concrete, such as foundations and reinforced slabs, use more cement per cubic meter — always follow the specification on your plans if one exists.
The calculator first computes the volume of the pour from its three dimensions, then multiplies that volume by fixed material coefficients: 320 kg of cement, 600 kg of sharp sand and 1200 kg of gravel per cubic meter, plus about 176 L of water. This gives a water-to-cement ratio of roughly 0.55, which produces a workable mix without being so wet that strength suffers.
Because the coefficients are per cubic meter, the results scale linearly: doubling the volume doubles every material quantity. That makes it easy to plan deliveries — for example, cement is commonly sold in 25 kg bags, so 320 kg of cement works out to about 13 bags per cubic meter.
Assumptions, limitations and practical tips
- Rectangular shapes only. The volume formula \( V = W \cdot H \cdot D \) assumes a simple box. For circular or tapered pours, use a dedicated tool such as the Concrete Column Fill calculator.
- General-purpose mix. The 1 : 2 : 4 proportions suit light-duty work. For structural elements, ask a professional or follow an engineer's specification, as the required strength may differ. See also our Concrete Ingredients calculator for a more detailed breakdown.
- Allow for waste. Add 5–10 % to the material quantities to cover spillage, uneven subgrade and mixing losses. It is much cheaper than ordering a second load mid-pour.
- Damp sand needs less water. If your sand is stored outside, reduce the added water accordingly; too much water weakens the cured concrete.
- Consistency matters. Measure materials by weight, not by shovelful, when strength is important. For other surface work, such as rendering walls, use the Cement and Sand for Plastering calculator instead.
If you only need the volume of concrete to order from a ready-mix supplier, the Concrete Volume calculator handles that in a single step.
Frequently Asked Questions
How many 25 kg bags of cement do I need per cubic meter of concrete?
At roughly 320 kg of cement per cubic meter, you need about 13 bags of 25 kg (or 7 bags of 50 kg) for every 1 m³ of finished concrete. For a smaller pour, divide accordingly — half a cubic meter needs around 6–7 bags of 25 kg. Always round up to whole bags and keep one spare in case of spillage or an uneven subgrade.
How do I convert the results to cubic feet or cubic yards?
1 cubic meter equals about 35.31 cubic feet or 1.31 cubic yards. So if your plans are in imperial units, multiply the volume in cubic feet by 0.0283 to get cubic meters before using the material quantities, or divide cubic yards by 1.31. The material outputs in kg can be converted at 1 kg ≈ 2.2 lb if you prefer pounds.
What water-to-cement ratio should I use, and why does it matter?
This calculator assumes a water-to-cement ratio of about 0.55 (176 L per 320 kg of cement), which balances workability and strength. Adding extra water makes concrete easier to place but significantly weakens it — more water means more pores and lower final strength. If your sand is damp from outdoor storage, cut the added water by 10–20 L per cubic meter to compensate.
Can I measure the mix by shovelfuls instead of by weight?
For light-duty work like paths and shed bases, a 1 : 2 : 4 ratio by shovelful is a common shortcut, but it is imprecise — shovel loads of sand, gravel and cement differ in weight. When strength matters, weigh the materials: use a bathroom scale or bucket with known volume and bulk density. A level bucket of cement weighs roughly 25 kg, which helps with batching.
How strong is a 1 : 2 : 4 concrete mix, and when do I need something stronger?
A 1 : 2 : 4 mix typically cures to around 15–20 MPa after 28 days, which is fine for patios, paths, kerbs and shed bases. Structural work — foundations, retaining walls, reinforced slabs and driveways carrying vehicles — usually needs a designated strength class (for example C25/30 or higher) with a higher cement content. Follow your engineer's specification or use ready-mix concrete for structural elements.
How long does concrete take to cure, and how should I look after it?
Concrete reaches about 70 % of its final strength after 7 days and full design strength at 28 days. Keep the surface damp for at least the first few days by covering it with plastic sheeting, damp hessian or a light water spray — this prevents rapid drying and cracking. Avoid walking on it for 24–48 hours and don't drive on a slab for at least 7 days, longer in cold weather.
What are the most common mistakes when mixing concrete by hand?
The biggest mistake is adding too much water, which severely weakens the mix. Others include mixing on bare soil (which contaminates the mix — use a board or mixer), using salty or dirty water, mixing unevenly so dry pockets remain, and pouring in very hot or freezing conditions. Also, only mix what you can place within about an hour, since concrete begins setting as soon as water is added.