How much mulch do I need for a garden bed?
Multiply the area of the bed by the depth you want. As a quick guide, one cubic yard of mulch covers about 108 square feet at 3 inches deep, or 162 square feet at 2 inches. The calculator above does the exact sum for your bed.
The right depth depends on what you are covering, and on whether you are starting a new bed or adding to mulch that is already there:
When you top up, check how deep the old mulch still is and enter only the extra depth you want to add. If you need help measuring the bed or choosing a depth, read our step-by-step guide to working out how much mulch you need.
How do you calculate mulch?
Mulch is sold by volume, so the job is to turn an area and a depth into cubic feet or cubic yards. Put both measurements in feet before you multiply. For a rectangular bed, the area is length × width.
Cubic feet = area (sq ft) × depth (in) ÷ 12
Cubic yards = cubic feet ÷ 27
Shortcut: cubic yards = area (sq ft) × depth (in) ÷ 324
Dividing the depth in inches by 12 turns it into feet. A cubic yard is 3 ft × 3 ft × 3 ft, which is 27 cubic feet. The shortcut simply combines both steps, because 12 × 27 = 324.
In metric, cubic metres = area (m²) × depth (cm) ÷ 100, and one cubic metre is 1,000 litres.
Fresh mulch settles in the first few weeks, and some always ends up on the lawn. Ticking the 10% box in the calculator multiplies the volume by 1.1 before it works out bags and cost.
Worked example: a 10 × 10 ft bed at 3 inches deep
With the 10% allowance switched on, the volume becomes 25 × 1.1 = 27.5 cubic feet, or 1.02 cubic yards. That is 14 bags of 2 cu ft or 10 bags of 3 cu ft, which is what the calculator shows for this bed.
How many bags of mulch do I need?
Divide the volume in cubic feet by the size printed on the bag, then round up to a whole bag. Bagged mulch is commonly sold in 2 and 3 cubic foot bags, and you can pick either size in the calculator.
Bags = cubic feet ÷ bag size (cu ft), rounded up
One cubic yard is 27 cubic feet, so it takes 13.5 bags of 2 cu ft (buy 14) or exactly 9 bags of 3 cu ft to make a cubic yard.
How many bags for 100 square feet?
These counts leave out the 10% allowance. With it, you need 10 bags of 2 cu ft at 2 inches and 14 bags at 3 inches.
Bags or bulk?
Bags are easy to carry and store, so they suit small beds and top-ups. For bigger jobs, bulk mulch sold by the cubic yard is usually cheaper and leaves no plastic to throw away. Once your order passes about a cubic yard, which is 14 bags of 2 cu ft, it is worth asking a supplier for a bulk price. In metric, one cubic metre fills twenty 50 L bags. Our guide compares bulk delivery and bagged mulch in more detail, from getting it home to storing it.
Mulch coverage and conversion chart
How far a cubic yard or a bag goes depends only on the depth. The figures below leave out the 10% allowance.
Coverage by depth
Cubic yards, cubic feet and bags
Bag counts are rounded up to whole bags.
How much will the mulch cost?
Enter a price in the optional box and choose how your supplier charges:
The estimate covers the mulch only. Delivery charges and minimum orders vary between suppliers, and bulk mulch may be sold in whole or half-yard steps, so check the final quote before you pay.
Circular beds, tree rings, paths and curved borders
For one or more rectangles, choose Length × width and use + Add another area for each extra section. Each area can have its own unit, and the calculator adds them up. For circles and other shapes, find the square footage first and enter it in Total area.
Circular beds
Area = 3.14 × radius × radius, where the radius is half the distance across. An 8 ft round bed has a radius of 4 ft, so 3.14 × 4 × 4 = 50.3 sq ft. At 3 inches deep with the 10% allowance, that is 0.51 cubic yards, or 7 bags of 2 cu ft.
Tree rings
Mulch the ring around the tree, not the trunk. Leave a few inches of bare soil around the base and never pile mulch against the bark. To find the ring area, take the bare circle away from the outer circle: area = 3.14 × (outer radius² − inner radius²).
For a ring 6 ft across around a trunk 1 ft wide, with a 3 inch gap, the outer radius is 3 ft and the inner radius is 0.75 ft. That gives 3.14 × (9 − 0.56) = about 26.5 sq ft. At 3 inches deep with 10% extra, you need 0.27 cubic yards, or 4 bags of 2 cu ft.
Paths
Multiply the length by the width. A path 3 ft wide and 50 ft long is 150 sq ft. At 2 inches deep that is 25 cubic feet, or 0.93 cubic yards. With 10% extra, the calculator gives 1.02 cubic yards, or 14 bags of 2 cu ft.
Curved or irregular borders
Split the bed into simple shapes, such as rectangles and half circles. Rectangles can go straight into Length × width as separate areas; work out any curved parts separately and add them to the total. For a long curving border, measure the length along the middle, take the average of a few width measurements and enter those as one area.
Does the type of mulch change how much I need?
No. A 3 inch layer over 100 square feet needs 25 cubic feet whether you use bark nuggets, shredded hardwood or wood chip. What differs is how much the layer settles. Fine shredded mulch tends to pack down more than coarse nuggets, so keep the 10% allowance for shredded types. Weight also varies between materials, which matters when you load a trailer, but bags and bulk orders are both sold by volume. The guide also explains how wood chips, bark and straw behave once spread.
What mulch does
Mulch is any layer you spread over bare soil. Bark, wood chip, leaves and compost are the common ones. A good layer does four jobs at once.
What types of mulch are there?
Organic mulch breaks down and improves the soil, so you top it up every year or two. Inorganic mulch lasts longer but adds nothing to the soil.
Organic
Bark
Coarse and slow to break down. Looks tidy for two to three years.
Best for shrub beds and borders
Wood chip
Cheaper than bark and often free from tree surgeons. Rots faster.
Best for paths and under trees
Leaves
Shred them first or they mat together and block water.
Best for vegetable beds over winter
Grass clippings
Rich in nitrogen. Dry them before use and spread thinly.
Best for quick cover between crops
Inorganic
Rubber crumb
Soft and long lasting, but it never feeds the soil.
Best for play areas
Gravel over fabric
Almost no upkeep. Hard to remove if you change your mind.
Best for dry, low planting
When should I mulch?
Late spring is the usual time, once the soil has warmed up and is still moist. A second layer in autumn protects roots through the winter. Always water dry soil before you spread mulch, because the layer will keep the dryness in as well.
Mulch calculator questions
Why does the calculator show more bags than my own sum?
It rounds up to whole bags, and if the 10% box is ticked it adds the extra before rounding. Untick the box to see the bare volume.
Should I measure the depth before or after the mulch settles?
Recommended depths refer to the settled layer. Fresh mulch looks deeper on the first day and sinks as it settles, which is another reason the 10% allowance helps. If you are adding to an old layer, check how much is left before you top it up.
Can I use metres and litres instead?
Yes. Switch Units to Metric and enter the area in square metres and the depth in centimetres. The results come out in cubic metres, litres and 50 L bags.