Concrete Slab Calculator - Work Out Exact Quantities for Your Project

To calculate concrete for a slab: 1) Measure length and width in metres, 2) Determine thickness (typically 100-150mm), 3) Convert thickness to metres (100mm = 0.1m), 4) Multiply: Length × Width × Thickness = Cubic metres, 5) Add 5-10% for waste. Example: 3m × 4m patio, 100mm thick: 3 × 4 × 0.1 = 1.2 cubic metres + 10% = 1.32 cubic metres. Our calculator does this instantly, showing results in cubic metres, cubic yards, and bags needed.

Bags needed depend on slab size and bag weight. A 25kg bag yields approximately 0.0125 cubic metres, so 1 cubic metre requires 80 bags (25kg). Example calculations: 1m² slab, 100mm thick = 0.1 cubic metres = 8 bags (25kg); 10m² slab, 100mm thick = 1.0 cubic metres = 80 bags (25kg). Our slab calculator shows exact bag requirements for 20kg, 25kg, and 40kg bags, helping you choose based on budget and handling preference.

UK concrete costs vary by region and supplier: Ready-mix concrete costs £65-100 per cubic metre, bagged concrete costs £3-5 per 25kg bag (£240-400 per cubic metre), and delivery charges range from £50-150 depending on distance. Example: 3m × 4m patio (1.2 cubic metres) - Ready-mix option: £78-120, Bagged option: £288-480 (96 bags). For small projects under 1 cubic metre, bags are more practical. Our calculator provides cost estimates based on your local prices.

Yes, DIY concrete slabs are achievable for small to medium projects. Suitable for DIY: Garden patios (under 10m²), shed bases (under 6m²), and small pathways. Requires professional: Large driveways (over 20m²), structural slabs, and slabs with complex drainage. DIY Tips: Use our calculator to order exact quantities, prepare ground with MOT Type 1 sub-base, install edge formwork, consider hiring a concrete mixer for quantities over 0.5 cubic metres, and work with a helper for efficient laying. Our PDF report provides a professional specification to show builders merchants.

Reinforcement requirements depend on slab use. Mesh reinforcement recommended for: Driveways (A142 or A193 mesh), garage floors (A142 mesh), and large patios over 15m² (A98 or A142 mesh). May not need reinforcement: Small garden patios under 10m², pathways, and shed bases. Reinforcement benefits include preventing cracking, distributing loads, and increasing lifespan. Place mesh in the middle-third of slab depth. Our calculator calculates concrete quantity only; consult a structural engineer for reinforcement specifications.

Concrete slab curing timeline: Initial set (24-48 hours) - can walk on surface carefully, keep covered and moist; Light use (7 days) - suitable for light foot traffic, continue moisture curing; Full cure (28 days) - reaches full strength, safe for vehicle traffic (driveways), can apply sealers or coatings. UK weather considerations: Avoid laying in freezing conditions (below 5°C), protect from rain for first 24 hours, cover with plastic sheeting to retain moisture, and in hot weather, mist regularly to prevent cracking. Use our slab calculator to plan material quantities, then schedule your project for suitable weather conditions.