Mulch Calculator
Enter the length and width of the bed, the depth of mulch you want and the volume printed on one bag. The calculator gives the volume of mulch in cubic feet and cubic yards, or cubic metres, and the number of bags.
Answer
You need
25bags
50 cu ft of mulch — 1.85 cu yd if you order in bulk.
- sq ft of bed
- 200
- cu ft of mulch
- 50
- cu yd for bulk
- 1.85
- cu ft left over
- 0
Check the work
Every line comes from the same calculation as the answer.
volume = length × width × depth
| depth | 3 ÷ 12 | 0.25 ft |
|---|---|---|
| area | 10 × 20 | 200 sq ft |
| volume | 200 × 0.25 | 50 cu ft |
| bulk | 50 ÷ 27 | 1.8519 cu yd |
| bags | ⌈ 50 ÷ 2 ⌉ | 25 |
How it works
Mulch is spread to a depth, so the amount is the bed area times that depth. A bed 10 by 20 feet covered 3 inches deep holds 200 square feet × 0.25 feet = 50 cubic feet. Bulk suppliers sell by the cubic yard, which is 27 cubic feet, and garden centres sell bags marked in cubic feet or litres.
Depth is the decision that drives the answer. Thinner layers are used to top up an existing bed, deeper ones to suppress weeds on bare soil. The calculator does not choose a depth for you; it shows how the volume changes as you change it.
Because the bed is measured as a rectangle, curved or irregular beds are best split into a few rectangles and the results added together. Mulch also settles after watering, which is one reason many gardeners round up generously.
Formula
volume = length × width × depth; bags = ⌈volume ÷ bag volume⌉
The bed area is multiplied by the depth in the same unit to give the volume, which is divided by the volume of one bag and rounded up.
Worked examples
- Try these numbers
Border 10 by 20 ft, 3 inches deep
- 3 inches is 0.25 ft; 10 × 20 × 0.25 = 50 cu ft.
- 50 ÷ 27 = 1.85 cubic yards for a bulk order.
- In 2 cu ft bags, 50 ÷ 2 = 25 bags exactly.
Buy 25 bags of 2 cu ft, or about 1.85 cu yd in bulk.
- Try these numbers
Metric bed, 4 by 2.5 m, 7.5 cm deep
- 7.5 cm is 0.075 m; 4 × 2.5 × 0.075 = 0.75 m³.
- 0.75 m³ is 750 litres; 750 ÷ 50 = 15 bags.
Buy 15 bags of 50 litres.
- Try these numbers
Small bed that needs part of a bag
- 6 × 3 ft at 3 inches deep is 18 × 0.25 = 4.5 cu ft.
- 4.5 ÷ 2 = 2.25 bags, rounded up to 3.
Buy 3 bags; 1.5 cu ft is left over.
Inputs and results
- Bed length
- One side of the bed, in feet or metres.
- Bed width
- The other side, in the same unit.
- Depth
- How thick the layer should be, in inches or centimetres.
- Bag volume
- Volume printed on one bag, in cubic feet or litres.
- Mulch volume
- Bed area times depth, in cubic feet and cubic yards, or cubic metres.
- Bags
- Volume divided by the bag volume, rounded up.
- Left over
- Mulch left in the last bag.
When to use it
- Buying bagged bark or wood chip for a new border.
- Deciding whether a bulk delivery by the cubic yard or cubic metre works out simpler than bags.
- Topping up an existing bed by a shallower depth than the original layer.
Common mistakes
- Entering depth in feet or metres instead of inches or centimetres: 3 inches is entered as 3.
- Comparing a bag in litres with a volume in cubic metres without converting; 1 cubic metre is 1,000 litres.
- Measuring the bed edge-to-edge including a path or lawn strip that will not be mulched.
What it does not do
- It treats the bed as one rectangle of even depth; it does not subtract plants, stones or tree trunks.
- It does not convert volume to weight. Bulk mulch weight varies with moisture and material.
- It does not recommend a depth for a particular plant or mulch type.
Method and assumptions
Depth is converted to the bed’s unit (12 inches to the foot, 100 centimetres to the metre) and multiplied by length and width. Imperial volumes are also shown in cubic yards, dividing cubic feet by 27.
Bag volumes in litres are converted to cubic metres (1,000 litres each) before dividing. The bag count is rounded up to whole bags.
Assumptions
- The bed is a rectangle covered to an even depth.
- Bag volume is the loose volume printed on the bag.
- Bags are bought whole.
Edge cases
- A depth of 0 has no volume, so no answer is shown.
- When the volume divides exactly by the bag size, no mulch is left over.
- Very large beds give many bags; the cubic-yard or cubic-metre figure is what a bulk supplier will ask for.
Sources and corrections
This calculator uses an elementary formula, so it needs no outside data source. The method, the rounding rules and how a reported error is corrected are set out in the site standards.
Result looks wrong?
Send the inputs you used and the answer you expected. Every report is checked against the formula and its tests, and confirmed errors are corrected in public.