Compost calculator
Enter the bed area and how deep a layer of compost you want to add. You'll get the volume and bag count.
Top-dress beds with 2–5 cm (1–2 in) of compost per season.
How this is calculated
Volume = area × depth ÷ 12. A 1–2 in top-dressing once or twice a year is plenty for most vegetable beds; work it into the top inch or leave it for worms to pull down. For a brand-new bed, 2–3 in dug in is reasonable.
Common questions
How often should I apply compost?
Once or twice a year is plenty for an established vegetable bed - in spring before planting and again after a heavy feeder like tomatoes or corn finishes. A brand-new bed benefits from a deeper one-time application dug in at the start.
Can I use too much compost?
Yes. More than about 3 in worked in at once can push soil nitrogen and salts higher than most vegetables want, and it wastes compost that would do more good spread over a couple of seasons. Stick to a 1-2 in top-dress in established beds.
Does compost replace fertilizer?
Partly. Compost feeds soil life and adds a slow, broad range of nutrients, but it's usually not concentrated enough on its own for heavy feeders like tomatoes and corn - see the fertilizer calculator to fill that gap.