Concrete Yardage Calculator — Slabs, Post Holes & Footings
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| Item | Volume (yd³) | Volume (m³) | Actions |
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How this Concrete Calculator Works
Volume = area × thickness. For rectangular slabs we multiply length by width to get area, then multiply by thickness. For trench footings we use total trench length × trench width × depth. For round columns and post holes we use the cylinder formula \(V = \pi r^2 h\). Inputs can be in imperial (feet/inches, cubic yards) or metric (metres/centimetres, cubic metres). We convert internally and display both yd³ and m³ so you can order locally.
Waste / over-order: concrete placement isn’t perfectly efficient. Subgrades aren’t laser-flat, holes cave slightly, and pumps/hoses hold some mix. A conservative 5–10% extra is common for small projects. Larger pours or complex formwork may warrant a different margin—ask your supplier if unsure.
Bag estimates: Bagged premix lists a typical yield (volume after mixing). Popular sizes and typical yields are: 40 lb ≈ 0.30 ft³, 50 lb ≈ 0.375 ft³, 60 lb ≈ 0.45 ft³, 80 lb ≈ 0.60 ft³, 90 lb ≈ 0.675 ft³. Metric bags: 20 kg ≈ 0.009 m³, 25 kg ≈ 0.011 m³, 30 kg ≈ 0.013 m³. Brands vary slightly with blend, aggregate, and water content—always order using the yield on your bag or supplier sheet. For ready-mix trucks, most suppliers quote and deliver in cubic metres or cubic yards.
Common thicknesses: garden paths/shed pads are often 75–100 mm (3–4 in); driveways 100–125 mm (4–5 in) with reinforcement and proper base; structural footings and columns should follow engineer/authority guidance. Depth to frost line varies by region—check local code.
Tips: compact a granular base and screed forms to consistent height to reduce waste. If you’re close to a bag boundary, buy one extra—running short is costlier than having a spare. Keep a small project list handy (stepping stones, fence repair) to use leftover mix.