The formula
How it works
Find out how much mulch you need to cover a garden bed to a chosen depth. The calculator gives the volume in cubic yards or cubic metres and the number of standard bags, so you can order the right amount in one trip.
FAQ
How deep should mulch be?
Two to three inches (about 5–8 cm) is right for most beds — enough to suppress weeds and hold moisture without smothering plants. Go a little thinner right around stems and trunks.
Bags or bulk?
Bags suit small beds and are easy to carry, but for anything over about two cubic yards, bulk delivery is usually cheaper. The calculator shows both the volume and a bag count so you can compare.
How often should I replace mulch?
Most organic mulches need topping up once a year, since they gradually break down and enrich the soil. A thin refresh layer is often enough rather than removing and replacing the whole depth.
Does the type of mulch change how much I need?
The volume calculation is the same regardless of material, but denser mulches like shredded hardwood settle less than light materials like straw, so you may need to add slightly more of a loose material over time.
Should I remove old mulch before adding new?
Usually not — a couple of inches of old, partly decomposed mulch is fine to leave, since removing it wastes the organic matter it has already added to the soil. Just rake it to break up any compacted crust before adding fresh mulch.
How much does mulch weigh?
A cubic yard of bark or wood mulch typically weighs 400 to 800 pounds depending on how wet it is, while a 2-cubic-foot bag weighs roughly 20 to 50 pounds. This matters for figuring out delivery and how much your vehicle can carry.
Can I use this calculator for irregularly shaped beds?
Yes — split the bed into simpler rectangles or circles, calculate the volume needed for each section separately, then add the results together for the total amount to order.
About the mulch calculator
This calculator works out how much mulch you need to cover a garden bed, from its length, width and the depth you want to lay. Mulch keeps down weeds, locks in moisture and tidies up a border, but it is sold by volume — cubic yards, cubic metres or bags — which makes the amount hard to picture. Turning your bed’s dimensions into a volume takes the guesswork out and stops you over- or under-ordering.
How to use it
Choose imperial or metric units, then enter the length and width of the bed and how deep you want the mulch. The calculator returns the volume and the number of standard bags. For example, a 20 ft by 10 ft bed covered 3 inches deep needs about 1.85 cubic yards, or roughly 25 two-cubic-foot bags. For an irregular bed, split it into rectangles, work out each, and add the volumes together before you order.
The formula
Volume is length times width times depth, , with the depth converted to the same unit as the length and width. In imperial, the depth in inches is divided by 12 to get feet, and the cubic-foot result is divided by 27 to reach cubic yards. Bag counts come from dividing the volume by a bag’s size — a common bag holds two cubic feet, so it takes 13.5 bags to make a cubic yard.
Where it is used
Gardeners and landscapers use it every spring to refresh beds and borders, and to price up mulching a whole yard. It helps decide between buying bags and ordering bulk, since the volume makes the cost comparison clear. The same length-by-width-by-depth calculation covers compost, topsoil, bark chips and decorative stone, making it a handy tool for any material spread evenly over the ground.