Compost Calculator
Compost is the simplest way to improve almost any soil. Enter your area and the layer you want to add to see how much compost to buy in bulk yards, cubic metres or bags.
View formula
How to use the Compost Calculator
- Choose the area shape and enter its size.
- Enter the compost depth: thin for lawns, thicker for new or poor beds.
- Choose your bag size if buying bagged compost.
- Press Calculate.
How much compost should I add?
| Use | Layer | Approx. per 100 sq ft |
|---|---|---|
| Lawn top-dressing | ¼ to ½ in | 2 to 4 cu ft |
| Established beds (yearly) | 1 in | 8.3 cu ft |
| New or poor beds | 2 to 3 in, mixed in | 17 to 25 cu ft |
| Raised-bed refresh | 1 to 2 in | 8 to 17 cu ft |
Worked example
Adding 2 inches of compost to 300 sq ft of new vegetable beds:
- Volume: 300 × 2 ÷ 12 = 50 cu ft
- Cubic yards: 50 ÷ 27 = 1.85 cu yd
- 1 cu ft bags: 50 bags: at this size bulk delivery is usually better value.
Tips
- Spread compost on the surface and gently fork it into the top 6 to 8 inches of new beds; on established beds you can simply leave it on top for worms to incorporate.
- Use only well-finished compost, it should smell earthy and look dark and crumbly.
- For lawns, rake compost in thin layers into the grass after aerating so it reaches the root zone.
FAQ
Compost Calculator: frequently asked questions
How much area does a yard of compost cover?
One cubic yard covers about 324 sq ft at 1 inch, 162 sq ft at 2 inches or roughly 1,300 sq ft at ¼ inch for lawn top-dressing.
Can you add too much compost?
Yes. Very heavy, repeated applications can raise phosphorus and salt levels. 1 to 2 inches a year is plenty for most established beds; a soil test helps if you apply compost often.
Is compost the same as topsoil?
No. Compost is decomposed organic matter used to improve soil; topsoil is mineral soil used to build up grade or fill. Many raised-bed mixes blend the two.
When should I add compost?
Autumn or early spring are ideal for beds. For lawns, top-dress after core aeration in the growing season.
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