Use the free tool below: your data never leaves your browser — all work happens on your device, and nothing is uploaded to any server.
How much mulch do you need
Mulch is the easiest upgrade a garden can get: it holds water in the soil, stops weeds, and keeps roots cool in summer and warmer in winter. The hard part is buying the right amount. Buy too little and beds end up patchy, with bare soil drying out between thin spots. Buy too much and bags pile up in the shed. This calculator turns your bed area and mulch depth into cubic yards, cubic metres, litres, and bag counts.
Enter the area to cover, pick square feet or square metres, enter the depth, pick inches or centimetres, and choose whether to show the headline volume in cubic yards or cubic metres. The calculator shows all units anyway, plus the number of 56-litre and 40-litre bags to buy. That unit flexibility is deliberate: suppliers sell mulch in different units in different countries.
A worked example
Take a bed of 100 square feet covered 3 inches deep. Multiply area by depth in feet: 100 times 0.25 feet gives 25 cubic feet. Divide by 27 and you get about 0.93 cubic yards. In litres that is about 708 litres, which means 13 bags of 56 litres or 18 bags of 40 litres. Round bags up, because a half-empty bag at the end of the job helps nobody.
Now try metric: a bed of 10 square metres covered 7.5 centimetres deep. Multiply 10 by 0.075 metres and you get 0.75 cubic metres, or 750 litres. That is 14 bags of 56 litres or 19 bags of 40 litres. Notice how close the two examples are: 100 square feet at 3 inches is nearly the same job as 10 square metres at 7.5 centimetres.
How deep should mulch be
For most beds, 5 to 8 centimetres, or about 2 to 3 inches, is right. Thinner mulch lets weeds through and dries out fast. Thicker mulch, above 10 centimetres, can block water and air from reaching the soil, and it wastes money. Vegetable beds need less mulch than shrub beds, because vegetables are replanted often and thick mulch gets in the way.
Paths and play areas can take deeper mulch, since nothing grows there and the goal is weed control and soft footing. Wood chip paths at 10 centimetres deep last well and feel good underfoot. Top paths up yearly, since wood chip breaks down and thins.
Keep mulch off stems and trunks
The most damaging mulch mistake is piling it against plant stems and tree trunks, forming a volcano shape. Mulch against bark traps moisture, rots the bark, and invites pests and disease. Keep mulch a few centimetres away from stems and trunks, and taper it thinner near the plant. The root zone still gets covered, but the bark stays dry.
Check mulch depth after heavy rain, which washes fine mulch into low spots and leaves high spots bare. Rake it level again and top up thin patches. Mulch breaks down over time, feeding the soil as it goes, so plan to top up every year rather than expecting one application to last forever.
Which mulch to choose
Bark chips last longest and suit shrubs and trees. Straw suits vegetable beds because it breaks down fast and adds organic matter, but it can carry weed seeds if it is not clean. Compost as mulch feeds the soil fastest but disappears within a season. Leaves are free and excellent, though they mat together when wet, so shred them first.
Stone mulch never breaks down, which sounds good until you try to plant through it or remove it. Stones also heat up in sun and cook shallow roots. Use stone only for paths and dry areas where nothing will ever be planted.
Frequently asked questions
Can I mulch over weeds? Pull tall weeds first, then lay cardboard over the rest and mulch on top. The cardboard smothers weeds and rots away within a season. Mulch alone over tall weeds just hides them for a week.
Does mulch steal nitrogen? Fresh wood chip on the surface can pull a little nitrogen from the top layer of soil as it breaks down, but this matters mainly for seedlings. Add a little compost under wood mulch in vegetable beds, and the problem disappears.
When should I mulch? Spring, after the soil warms up, is the best time for most beds. Mulching cold spring soil too early keeps it cold and delays growth. Autumn mulching protects roots over winter and is the second-best time.
Use the calculator above with your real bed area and depth, keep mulch off bark, and top up every year. Garden results are general guidance estimates only. Your local climate, your soil, and the instructions on your seed packets govern what actually grows, and results vary with weather and conditions.