Cement Sand Stone Calculator

A cement sand stone calculator is for concrete - slabs, footings, paths and bases - which needs three ingredients: cement, sand and coarse aggregate (stone/gravel). A mortar calculator (used for bricklaying or rendering) mixes only cement and sand, with no stone, because mortar bonds bricks or blocks together rather than filling a structural slab. Using a two-part mortar mix where a job actually needs three-part concrete will produce a weak, aggregate-free mix that isn't suitable for load-bearing or ground-contact work.

1:2:4 (cement:sand:stone) is the widely used UK default for general-purpose work - foundations, garden slabs and paths - and is this calculator's starting selection. Step up to the stronger 1:1.5:3 mix for driveways, garage floors or anything structural that takes vehicle weight or heavy load. Step down to the weaker, cheaper 1:3:6 mix for mass-fill jobs that don't need much strength, such as blinding a footing, bedding a manhole cover, or backfilling a trench.

10% is a commonly used default that covers spillage, mixing losses and minor over-excavation. Use 15% if you're a first-time DIYer, working ground that's uneven or hard to screed accurately, or simply want a comfortable buffer rather than an emergency mid-pour trip to the merchant.

The calculator multiplies your length, width and thickness to get the wet (finished) concrete volume, adds your chosen waste margin, then multiplies by a 1.54 bulking factor to get the dry material volume - because loose, dry cement, sand and stone take up more space than the same materials once mixed, placed and compacted. That dry volume is then split across your chosen mix ratio's parts (for example, 1:2:4 splits it into 7ths: 1 part cement, 2 parts sand, 4 parts stone).

Builders' merchants sell sand and aggregate either loose by the tonne or pre-packed in a "bulk" or "jumbo" bag holding roughly 800kg. This calculator shows both so you can order however your local merchant sells it - note that bulk bag weight varies by supplier (commonly 800kg-1000kg), so check the exact figure before ordering if you're close to a bag boundary.

20mm graded aggregate is the standard general-purpose size for most domestic concrete - slabs, footings and paths. A finer 10mm aggregate is sometimes preferred for thin slabs (under roughly 75mm) or where a smoother finish matters, since larger stones can be harder to screed flat in a thin layer; check with your merchant if your slab is unusually thin.

As of August 2026, a 25kg bag of cement typically costs roughly £6-£9.50, a bulk bag (~800kg) of sharp sand roughly £45-£65, and a bulk bag of 20mm aggregate roughly £70-£100, based on current UK builders' merchant listings - so a typical small slab's materials often land in the £400-£550 range before delivery. Enter your own supplier's prices above for an estimate specific to your job; this calculator never assumes default prices.

For pours above roughly 2m³, ready-mix is often more practical: hand-mixing that much concrete in a domestic mixer is a substantial job, and standard C25/C30 ready-mix delivered typically costs £100-£165 per m³ in the UK as of 2026, per MyBuilder's ready-mix price guide. Most suppliers set a 3-4m³ minimum order, though, and will charge a £30-£60 per m³ surcharge (or a flat £200-300 minimum charge) on smaller loads - so for a small job well under that minimum, bagged materials are usually still the cheaper route.

This calculator estimates the concrete mix only, not reinforcement. Most domestic slabs, paths and shed bases don't need steel reinforcement, but driveways, anything taking vehicle load, or a slab over unstable or variable ground often benefit from or require mesh reinforcement - check building regulations guidance or a structural engineer for anything load-bearing or unusual.

Most domestic slabs sit on a compacted hardcore or Type 1 sub-base (commonly 100-150mm deep, more for a driveway) beneath the concrete itself, to provide a stable, well-drained base and stop the slab cracking or settling unevenly. This calculator doesn't estimate sub-base materials - only the concrete mix on top of it.

Yes for a shed base slab - treat it as a simple rectangular pour at your chosen thickness (typically 75-100mm for a light shed, more for a heavier building). For fence post holes, CoryVu's ballast and cement calculator for a shed base is a closer fit for small pours, since posts need a different volume calculation (roughly a cylinder or cone per hole) rather than a flat rectangular slab.

This calculator assumes a full-depth new pour. For a thin topping layer or patch repair, use your patch's actual thickness as the thickness input - the same volume-to-materials calculation applies, but very thin toppings (under about 40mm) usually need a bonding agent and finer aggregate or a screed mix rather than standard 20mm-aggregate concrete.

Concrete reaches a walkable initial set within about 24-48 hours in normal UK weather, but continues gaining strength for around 28 days, similar to mortar. Avoid driving on or heavily loading a new slab until at least 7 days have passed, and protect fresh concrete from frost, heavy rain and fast drying (cover it) in the first 24-48 hours, since any of those can weaken or crack the surface.

No. It estimates bagged materials from widely used UK nominal concrete mix ratios and standard bulk densities. It is not a substitute for a structural engineer's assessment on anything load-bearing, a designed strength-class mix (such as an engineer-specified C25/C30 mix), or building regulations and planning permission guidance, which depend on your specific project and local authority.

This calculator uses metric units throughout (metres and millimetres for dimensions, kilograms and tonnes for materials), matching how UK builders' merchants sell cement, sand and aggregate. If you're working in imperial measurements, convert your dimensions to metres first (1 foot is approximately 0.3048m).