Kalkulator Volume Beton

How much concrete do I need for a 10×10 slab?

A 10×10 foot slab is one of the most common residential concrete pours — used for patios, shed bases, and small garage pads. To calculate the volume, multiply length × width × depth. For a standard 4-inch (0.33 ft) thick slab: 10 × 10 × 0.33 = 33.3 cubic feet, or about 1.23 cubic yards. In metric terms, that is roughly 3.05 × 3.05 × 0.1 = 0.93 cubic metres.

At a concrete density of approximately 2,400 kg/m³ (about 4,050 lb/yd³), this slab would require roughly 2,232 kg (4,920 lb) of mixed concrete. If you are using pre-mixed bags rather than ordering ready-mix, you would need approximately 90 bags at 25 kg each, 56 bags at 40 kg, or 45 bags at 50 kg — before accounting for waste.

Always add a waste factor. For a simple rectangular slab on well-prepared, level ground, 5% waste is usually adequate. For slabs with irregular edges, sloped subgrade, or inexperienced crews, increase to 10-15%. Our calculator applies waste automatically so you order the right quantity the first time.

How to calculate concrete for a circular footing

Circular footings — also called pier footings, column pads, or sonotube fills — are common in deck construction, fence posts, and light structural foundations. The volume formula is π × r² × depth, where r is the radius (half the diameter). For example, a 12-inch (0.3 m) diameter sonotube that is 4 feet (1.22 m) deep contains π × 0.15² × 1.22 = 0.086 m³, or roughly 207 kg of concrete — about 9 bags at 25 kg each.

When calculating for multiple footings, compute the volume for one footing and multiply by the number of piers. It is more efficient to order a slightly larger total quantity than to run short mid-pour, as cold joints between pours weaken the structural connection. If you have 12 identical footings, calculate one and multiply by 12, then add your waste factor to the total.

For bell-shaped or stepped footings where the bottom flares out wider than the top, break the shape into a cylinder plus a truncated cone and add the volumes together. Alternatively, use the trapezoidal mode in our calculator as a reasonable approximation for tapered shapes.

What waste factor should I use?

The waste factor accounts for concrete that does not end up in your finished pour. Sources of waste include: spillage during mixing and transport, over-excavation of the subgrade (meaning the hole is deeper or wider than planned), material left in the mixer or wheelbarrow, and over-filling of formwork due to bowing or imperfect levelling.

As a general guide: use 5% for simple, well-formed rectangular slabs on flat, compacted ground with experienced workers. Use 10% (the default in our calculator) for typical residential projects with standard formwork. Use 15% for irregular shapes, sloped sites, first-time DIY pours, or when the subgrade has not been professionally prepared.

Professional ready-mix suppliers typically recommend ordering 5-10% more than calculated volume. For bag concrete, rounding up to the nearest full bag is usually sufficient — our calculator already applies ceiling rounding after adding the waste factor. Running short is almost always more expensive than having a small surplus, because a partial second delivery or an extra trip to the hardware store adds cost and risks a cold joint in your pour.

Volume formulas at a glance

Rectangular: Volume = Length × Width × Depth. This covers slabs, footings, walls, and beams — any shape with a uniform rectangular cross-section.

Circular: Volume = π × (Diameter / 2)² × Depth. Used for round columns, sonotubes, cylindrical tanks, and round footings.

Trapezoidal: Volume = ((Top Width + Bottom Width) / 2) × Depth × Length. This covers tapered walls, channel linings, retaining wall bases, and any shape where two parallel sides have different widths.

After computing the raw volume, multiply by the concrete density (approximately 2,400 kg/m³ for normal-weight concrete) to get the total mass, then divide by your chosen bag size and round up to get the number of bags needed. Do not forget to include the waste factor before dividing by bag size.