GardenCalcs.uk
Mulch Calculator — How Much Mulch Do I Need
Calculate mulch quantities for beds, borders, and paths.
Length of the bed, border or path to be mulched
Width of the area; for an irregular bed, use the average width
Layer depth. RHS suggests 5-7.5 cm for organic mulch; up to 8-12 cm for coarse wood chips
Pick a preset, or choose Custom and enter a bulk density in kg/m³ (organic mulch ~300-500, decorative gravel/stone ~1400-1500)
Optional: price of one retail bag, to estimate total cost
Adds 10% to cover settling, uneven beds and topping-up around plants
Default: 60 litres
Default: 0.85 m³
How We Calculate This
Volume is calculated as: Length × Width × Depth (converted to metres).
The calculator converts volume into 60-litre bags (a common retail size) and bulk bags (0.85 m³).
Weight is estimated using typical densities: bark ~350 kg/m³, wood chip ~300 kg/m³, gravel ~1500 kg/m³, compost ~500 kg/m³.
Frequently Asked Questions
For weed suppression, lay mulch 5-7.5 cm (2-3 inches) deep. For decorative bark, 5 cm is usually sufficient. Avoid piling mulch against plant stems.
The best times are mid-to-late spring (when soil has warmed) and autumn. Mulching in spring helps retain moisture; autumn mulching protects roots from frost.
Bark mulch is popular for borders. Compost mulch feeds the soil. Wood chips suit paths. Gravel mulch works for Mediterranean-style planting or alpine beds.
Bark mulch typically lasts 2-3 years before needing topping up. Fine bark decomposes faster (1-2 years) while chunky bark lasts longer (3-4 years).
Usually no. If the old mulch has partially decomposed, it is feeding the soil. Simply top up to the desired depth. Only remove if it has become matted or diseased.
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Last updated: February 2026
All calculations are estimates based on standard gardening guidelines. Results may vary with soil conditions, climate, and plant varieties.