Mulch Calculator
Work out how much mulch your beds need, in cubic yards or bags, including topping up an existing layer, and compare bagged and bulk prices.
How to Use
- Pick the bed shape: rectangle, circle (around a tree) or a known area if you have several beds added up.
- Enter the sizes and the depth you want when you are finished, usually 2 to 3 inches.
- If old mulch is still there, enter its depth under Already there; only the difference is counted.
- Choose the bag size you can buy. Add a bag price and a bulk price per yard to compare them.
- Read the volume and the number of bags; Show Work lists every step.
Worked Example
A bed 20 ft long and 6 ft wide, mulched 3 in deep. Area = 20 × 6 = 120 ft². Depth = 3 ÷ 12 = 0.25 ft, so the volume is 120 × 0.25 = 30 ft³, which is 30 ÷ 27 = 1.11 yd³. In 2 ft³ bags: 30 ÷ 2 = 15 bags.
Topping up. If an inch of last year’s mulch is still there, only 2 more inches are needed: 120 × 2 ÷ 12 = 20 ft³, or 10 bags, a third less.
The common mistake: trusting the coverage on the bag. A 2 ft³ bag “covers 12 ft²” only at 2 inches deep. At 3 inches it covers 8 ft², so the 120 ft² bed needs 15 bags, not 10.
Show Work
Formulas
What Mulch Does
A layer of mulch shades the soil, so weed seeds that need light to germinate stay dormant; it slows evaporation, evens out soil temperature, and stops rain splashing soil onto leaves. Organic mulches such as shredded bark, wood chips, pine straw and compost also feed the soil as they break down, which is why they need topping up every year or two.
Deeper is not better. More than about 4 inches can keep roots from getting air and water, and mulch heaped against a trunk holds moisture against the bark. A ring 2 to 3 inches deep with a gap around the trunk does the job.
About This Calculator
This calculator finds the mulch for a rectangular or round bed, or any area you already know, at the depth you want, minus whatever is already there. It counts bags in US sizes (1.5, 2 and 3 ft³) or metric ones (50 to 100 litres), converts to cubic yards or cubic metres, and compares the cost of bags with bulk delivery.
Everything runs in your browser; nothing is sent anywhere.
Related calculators: Soil Calculator, Gravel Calculator, and Sod Calculator.
Frequently Asked Questions
How deep should mulch be?
Two to three inches (5–8 cm) is the usual depth for beds: enough to block light from weed seeds and hold moisture. Fine mulch can be thinner; coarse bark can go to 4 inches. Keep mulch a few inches away from tree trunks and plant stems, because a “volcano” piled against the bark keeps it wet and invites rot.
How much area does a bag of mulch cover?
A 2 ft³ bag covers 12 ft² at 2 inches deep, 8 ft² at 3 inches, and 6 ft² at 4 inches. Bag labels usually quote coverage at 2 inches, so check the depth before you rely on them.
How many bags of mulch are in a cubic yard?
A cubic yard is 27 ft³, so it equals 13.5 bags of 2 ft³ or 9 bags of 3 ft³. In metric, a cubic metre is twenty 50-litre bags.
How much does a cubic yard of mulch cover?
One cubic yard covers 162 ft² at 2 inches, 108 ft² at 3 inches and 81 ft² at 4 inches. A cubic metre covers 20 m² at 5 cm deep.
Is bulk mulch cheaper than bags?
Usually, once you need more than a cubic yard or two. Bulk mulch is sold by the yard and delivered or loaded into a truck; the same yard in bags costs 13.5 bags’ worth, often two or three times as much. Bags are handier for small beds and for carrying through a house.
How do I use the Mulch Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Does it cost anything or need an account?
No. The tool is completely free, there is no account to create, and it keeps working offline after the page first loads.
Is anything I type uploaded?
No. The tool works entirely on your device, so the values you enter never leave your browser.
Common Use Cases
Front bed
A 20×6 ft bed at 3 in needs 30 ft³: 1.11 yd³ or 15 bags of 2 ft³.
Topping up
The same bed with 1 in of old mulch left needs only 2 in more: 20 ft³, or 10 bags.
Tree ring
A 6 ft circle around a tree, 3 in deep, holds 7.07 ft³: 4 bags of 2 ft³.
Whole garden
Beds adding up to 900 ft² at 3 in need 8.33 yd³, which is 113 bags of 2 ft³; bulk is the clear choice.
Metric beds
12 m² of beds at 7.5 cm need 0.9 m³, eighteen 50-litre bags.
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