Loona Construction Calculators
Pouring a slab, footing or path? Enter its length, width and thickness in metres or feet and inches, and get the concrete volume in cubic metres and cubic yards — plus the number of pre-mix bags to buy if you are mixing it yourself instead of ordering ready-mix.
At 100 mm thick: 4 × 3 × 0.1 = 1.2 m³ exactly. Order 1.32 m³ with a 10% allowance for uneven ground and spillage — uneven sub-bases are the biggest cause of running short.
About 87 bags of 25 kg pre-mix, or about 59 bags of 80 lb pre-mix, per cubic metre placed. Beyond roughly half a cubic metre, ready-mix delivery is usually cheaper and far less work.
Paths and patios: 100 mm (4 in). Driveways: 125–150 mm (5–6 in) over a compacted sub-base. Sheds and light structures: 100–150 mm. Always check local requirements for structural work.
Concrete is simply a volume calculation, with standard yields for bagged pre-mix.
Volume = Length × Width × Thickness
Bags = Volume × (1 + Waste %) ÷ Yield per bag
Standard yields used: 25 kg bag ≈ 0.0115 m³, 20 kg bag ≈ 0.0092 m³, 80 lb bag ≈ 0.6 ft³ (0.0170 m³), 60 lb bag ≈ 0.45 ft³ (0.0127 m³). One cubic metre equals 1.308 cubic yards.
Ready-mix wins on consistency, speed and price for anything over about 0.5 m³, and the whole pour happens at once. Bags suit small, awkward jobs where a truck cannot reach or the volume is tiny.
Ground is never perfectly level, forms bulge slightly, and some concrete stays in the barrow and pump. Running short mid-pour leaves a weak cold joint — the extra is cheap insurance.
Yes — switch to Imperial for feet and inches; results show cubic yards alongside metres, and bag counts for US 60 lb and 80 lb pre-mix bags.
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