Mulch Calculator for Garden Beds
Calculate how many bags of mulch you need for a flower bed, garden or trees, with a 10% allowance.
Tip: For a 5 cm layer, 1 m³ of mulch covers about 20 m². Don't pile wet mulch against the plant's stem — leave a 3–5 cm gap to avoid rot.
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About this digital tool
Mulch (a protective layer of organic material or wood chips) keeps moisture in the soil, stops weeds growing and keeps the plant's roots cooler in summer. To buy the right amount, you need to know three things: the area of the bed in m², the thickness of the layer (usually 5–10 cm) and the volume of one bag. This calculator multiplies the area by the thickness to get the volume in m³, adds a 10% allowance for uneven ground and rounds up to a whole number of bags.
How to use
- Measure the length and width of the bed and calculate the area (m²)
- Enter the desired layer thickness in cm
- Enter the volume of one bag in litres (usually 40–70 L)
- Optional: enter the price of one bag to see the total cost
- See the number of bags to buy, rounded up
Frequently asked questions
How thick should the layer of mulch be?
For flower and vegetable beds, 5–7 cm is usually enough. For trees and shrubs, 7–10 cm. A layer thicker than 10 cm can block air and water reaching the soil.
How many bags of mulch do I need for 10 m²?
With a 5 cm layer: 10 m² × 0.05 m = 0.5 m³, plus a 10% allowance = 0.55 m³. With a 50 L bag, 11 bags are needed. The calculator does this automatically.
When should I renew the mulch?
Usually once a year. Organic mulch (bark, straw, leaves) breaks down into humus, so you should top it up every spring to maintain the thickness.
Which mulch is best for the bed?
Wood bark and chips last longer, straw and dry leaves break down faster but enrich the soil. Stone or gravel mulch is for beds without plants or for cacti.