Mulch Calculator
Calculate how many bags of wood chips or bark mulch you need for flower beds and planting areas, based on area and layer thickness.
How to use the mulch calculator
- Enter the length and width of the bed or planting area.
- Enter the desired layer thickness — 5-8 cm is common for effective weed suppression.
- The calculator shows volume in cubic meters and roughly how many 60-liter bags you need.
How the mulch amount is calculated
The volume is area times thickness, once the thickness is converted from centimeters to meters:
Wood chips and bark mulch are often sold in bags of around 50-70 liters. This calculator uses 60 liters (0.06 m³) as a typical average — check the bag size of the product you're buying for a more exact count.
Depth is what makes mulch work
Mulch is used mainly to suppress weeds and retain moisture, and both depend on a layer thick enough to actually block light. A thin layer looks tidy but lets through enough light for weeds to come up. Too thick a layer against stems and crowns, on the other hand, holds moisture against the plant and can cause rot — which is why mulch is normally kept slightly clear of trunks.
Mulch breaks down over time and needs topping up, typically every few years. That decomposition consumes nitrogen in the top layer of soil, which can leave plants in the bed looking paler in the first year — so beds being mulched for the first time are often fertilised at the same time. Coarse mulch breaks down more slowly and lasts longer, but covers less densely.
Frequently asked questions
What's the difference between wood chips and bark mulch?
Wood chips are made from ground-up wood, while bark mulch is a byproduct of debarking timber. Both work well as ground cover in beds, but can differ somewhat in how fast they break down and in appearance.
How often do I need to refill?
Depending on material and exposure, the mulch layer gradually breaks down, and most need refilling every 1-3 years to maintain the desired thickness and weed suppression.