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Estimate the volume and weight of a triangular windrow compost pile, the amount of compost needed for a target application rate, and the area one pile covers.
Enter windrow length, base width and height, target application rate (t/ha), compost density and field area. The calculator returns pile volume, weight, required amount and covered area.
You built a 20 m long, 2 m wide, 1.5 m tall windrow and guessed it would cover a hectare at 10 t/ha. The pile actually holds only 30 m³ and about 18 tonnes — enough for less than 2 ha, not the 10 ha you planned to cover.
✓ Expert Reviewed: This calculator and its content have been reviewed by agricultural experts. Formulas are based on standard extension service recommendations. For site-specific advice, consult your local agronomist.
Measure your windrow dimensions (length, base width, peak height), enter the target application rate in t/ha, compost density (600 kg/m³ is typical for finished compost) and field area. Click Calculate.
Windrow volume is computed as a triangular prism: cross-section area = 0.5 × base width × height; volume = length × cross-section. Weight = volume × bulk density. Finished compost typically weighs 500–700 kg/m³; fresh raw material is lighter at 300–400 kg/m³.
Volume = L × (0.5 × W × H). Weight (t) = Volume × Density (kg/m³) ÷ 1000. Required compost (t) = target rate (t/ha) × field area (ha). Area covered = pile weight ÷ target rate.
L = 20 m, W = 2 m, H = 1.5 m. Cross-section = 0.5 × 2 × 1.5 = 1.5 m². Volume = 20 × 1.5 = 30 m³. Weight = 30 × 600 ÷ 1000 = 18 t. At 10 t/ha, covers 1.8 ha.
Common mistakes: using a rectangular cross-section (overestimates volume), forgetting that finished compost loses 30–50% of its volume during curing, over-applying compost (P builds up rapidly), and not turning piles often enough. Thermophilic piles should be turned every 5–7 days to maintain 55–65 °C.
For thermophilic (hot) composting, turn every 5–7 days to keep temperatures at 55–65 °C and ensure even decomposition. In slow or cold composting, turn every 3–4 weeks. Use a thermometer: if the pile drops below 40 °C it is not actively composting.
Aerobic windrows should be at least 1 m wide × 1 m high (to heat up) but no wider than 2.5 m or higher than 1.5 m (to allow oxygen penetration). This calculator uses a triangular cross-section typical of windrow turners.
Typical agronomic rates are 5–20 t/ha (2–9 ton/acre). Apply no more than needed to supply P, because compost is rich in P and repeated applications build up soil P to environmentally problematic levels.
The ideal C:N ratio for composting is 25–30:1. Greens (manure, grass, food scraps) are 15:1; browns (straw, wood chips, leaves) are 80:1+. Mix roughly one volume of greens to three volumes of browns. A too-high C:N slows decomposition; too-low C:N produces ammonia odor.
Compost supplies N, P and K but slowly and at low concentrations (1-3% N, 0.5-2% P₂O₅, 1-2% K₂O). It is best used as a soil amendment to improve structure, water holding and biology, not as the sole nutrient source for high-yield crops.