How to use this calculator
Enter bed length, width and depth. Add an allowance if useful, then enter the volume printed on one bag in cubic feet or liters.
The math behind it
Volume = length × width × depth × (1 + allowance ÷ 100) Bags = round up(required volume ÷ volume per bag)
A worked example
A 10 ft × 12 ft bed with 3 in of mulch needs 30 ft³ without allowance. That is 15 bags of 2 ft³ each.
Assumptions & precision
Dimensions must be positive. Extra material allowance is a nonnegative percentage added once to geometric volume. Exact international foot = 0.3048 m; yard = 0.9144 m. Rectangular geometry only. Actual waste, settling, excavation and supplier increments vary. Unrounded intermediate values; results display up to 6 decimal places. Magnitudes above 10¹⁵ are rejected. Bag count rounds up after calculation; tiny floating-point noise at an exact whole-bag boundary is ignored. Bag volume must be positive.
A common question
What depth should I use?
Enter the intended depth for your planting and material. The example is 3 inches, not a recommendation for every plant or site.