Compost calculator
Compost goes on much thinner than mulch. A lawn topdressing is only 1/4–1/2 in; working compost into a new bed is typically 1–3 in, and more on very poor soil.
Enter your measurements
More options: Bag price · Bulk price · Sold by …
- Bags of that size
- 42 bags · 1 cu ft bag
- If you order bulk, ask for
- 2 cu yd
25 ft × 20 ft = 500 sq ft
500 sq ft × 1 in ÷ 12 = 41.7 cu ft ÷ 27 = 1.54 cu yd
41.7 cu ft ÷ 1 cu ft per bag = 42 bags
Bulk: 1.54 cu yd rounded up to the next ½ cu yd = 2 cu yd
Quick answers for common sizes
| Example | Answer |
|---|---|
| How much compost to topdress 1,000 sq ft of lawn | 0.77 cu yd |
| How much compost for a 100 sq ft vegetable garden | 0.62 cu yd |
Compost needed by depth
| Depth | Compost needed | Bags of that size |
|---|---|---|
| 0.25 in | 0.39 cu yd | 11 bags |
| 0.5 in | 0.77 cu yd | 21 bags |
| 1 in | 1.54 cu yd | 42 bags |
| 2 in | 3.09 cu yd | 84 bags |
| 3 in | 4.63 cu yd | 125 bags |
How much compost to use
The math is the same as for mulch — area × depth — but the depths are much smaller, and small depth errors make big volume differences. A quarter inch over 1,000 sq ft is under a cubic yard (27 cubic feet); three inches over the same area is more than nine.
cubic feet = area (sq ft) × depth (in) ÷ 12 cubic yards = cubic feet ÷ 27 1/4 in over 1,000 sq ft ≈ 20.8 cu ft ≈ 0.77 yd³
| Use | Typical depth | Per 1,000 sq ft |
|---|---|---|
| Lawn topdressing | 1/4 in | About 0.77 yd³ |
| Heavier lawn topdressing | 1/2 in | About 1.5 yd³ |
| Yearly top-up on vegetable beds | 1 in | About 3.1 yd³ |
| Amending a new bed (dig or till in) | 2–3 in | About 6.2–9.3 yd³ |
Two common jobs are worked through in full: How much compost to topdress 1,000 sq ft of lawn, including why a quarter inch is enough, and How much compost for a 100 sq ft vegetable garden, which is also about what three 4 × 8 raised beds need for a generous top-up.
Tips
- Compost quality varies a lot. Ask whether it is screened and fully finished — it should smell earthy, not sour or like ammonia.
- For lawns, topdress right after core aeration so compost falls into the holes.
- Heavy, repeated compost applications can build up phosphorus (P, the middle number on an N-P-K fertilizer label), and Oregon State University Extension notes the excess can wash out of the root zone. If a soil test shows high P, go lighter.
- Bagged compost is often sold by the cubic foot or by weight; if a bag lists only pounds, check the label for its volume.
Bagged or bulk compost?
Bagged compost is convenient for a bed or two, but it adds up fast: a single cubic yard is 27 bags of 1 cu ft. Many municipalities and landscape yards sell screened compost in bulk, and some give it away. Bulk usually sells in half- or whole-yard steps (0.5 or 1 m³ in metric), so the calculator prices it on the rounded-up order; the yard’s minimum, the truck size and the delivery fee go under More options. Bulk quality varies more than bagged, so look at it before you buy — it should be dark, crumbly and free of visible chunks of wood, plastic or rock. Homemade compost is ideal for topdressing beds; screen it through half-inch mesh if you are spreading it on a lawn.
CalculatorMulch Calculator →Mulching the same bed after amending it?What topdressing means, and how a cubic yard converts to bags, is covered in words you’ll hear at the yard.
What you’ll need
- Wheelbarrow (6 cu ft class)Mid-range price
Most home wheelbarrows hold 4–6 cubic feet — so a cubic yard of mulch is five or six trips. Two wheels are steadier on soft ground.
See options on Amazon (opens in a new tab) - Bow rake / landscape rakeBudget price
Steel tines for spreading gravel and soil and leveling it flat. The flat back of a bow rake doubles as a leveling tool.
See options on Amazon (opens in a new tab) - Compost bin or tumblerMid-range price
Turns yard waste into the compost the calculators keep telling you to buy. Tumblers are tidier; open bins handle more volume.
See options on Amazon (opens in a new tab) - Soil test kitBudget price
A quick read on pH and nutrients. For detailed results, many state extension labs offer inexpensive mail-in tests.
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Frequently asked questions
How much compost do I need to topdress 1,000 sq ft of lawn?
About 0.77 cubic yards at 1/4 in, and double that at 1/2 in. The full worked example is How much compost to topdress 1,000 sq ft of lawn.
How much compost should I add to a garden bed?
Oregon State University Extension suggests 1/4–1 in a year on existing beds, and 3–4 in worked into the top 8–12 in when building a new bed. See How much compost for a 100 sq ft vegetable garden for a worked example.
Can you put too much compost on a garden?
Yes. Very heavy yearly applications can raise phosphorus and salt levels. A soil test every few years is the easiest way to know when to back off.
Related guides
Sources
- Penn State Extension: Using Composts to Improve Turf Performance (opens in a new tab) — Topdress established turf about 1/4 in and work it in (ideally with core aeration); 1–2 in tilled 4–6 in deep before seeding or sodding.
- Oregon State University Extension: How to use compost in gardens and landscapes (EM 9308) (opens in a new tab) — New beds: 3–4 in worked into the top 8–12 in; existing beds: 1/4–1 in a year; lawns: 1/4–1/2 in; excess compost leaches nutrients.
- Gravel Monkey — How many tons of gravel in a dump truck? (opens in a new tab) — Typical payloads: single-axle about 6–10 tons, tandem 12–16, tri-axle 18–25; gravel hits the weight limit before the bed is full.