Compost Calculator – Volume, Cost & Weight

This compost calculator takes the guesswork out of planning your garden or landscaping project. Enter your area dimensions and desired application depth to instantly see exactly how much compost you need — along with an estimated total cost and total delivery weight. Whether you're filling a raised bed, top-dressing a lawn, or preparing a new planting area, this three-in-one tool gives you all the numbers you need before you place an order.

Most compost calculators only tell you the volume. This one goes further: once your volume is calculated, it works out your total spend based on the price you're paying per cubic meter or cubic foot, then estimates the weight of your order so you can plan access, transport, and storage accordingly. No more ordering too little, over-spending on excess material, or getting caught out by a delivery that's heavier than expected.

Compost is decomposed organic matter — kitchen scraps, garden clippings, leaves — transformed into a nutrient-rich soil amendment. Adding compost improves soil structure, feeds beneficial microbes, retains moisture, and provides slow-release nutrients that support plant growth for months after application.

The challenge is that compost is sold by volume — cubic yards, cubic meters, or liters — but your garden is measured in length and width. Bridging that gap is where most gardeners either underestimate or over-order. Getting the calculation right saves money, avoids unnecessary waste, and ensures your beds receive exactly the amendment depth they need for healthy plant growth.

The calculator works in three interconnected sections. Fill them in from top to bottom:

Section 1 – Compost Volume

1. Enter the length of your area and choose your preferred units (centimeters, meters, feet, inches, or yards)
2. Enter the width in your chosen units — your total area calculates automatically
3. Enter the depth of compost you want to apply — the volume result appears instantly

Section 2 – Compost Cost

4. Enter the price per unit you've been quoted by your supplier (per m³, per cubic yard, etc.)
5. Your total cost appears, calculated automatically from the volume above

Section 3 – Compost Weight

6. Enter the density of your compost in kg/m³ (your supplier can provide this, or use 650 kg/m³ as a typical starting point)
7. Your total weight appears — useful for planning deliveries and checking vehicle load limits

Change any value and all results update immediately. You can also switch units at any point to see results in a different measurement system.

The calculation behind the tool is straightforward:

Volume = Length × Width × Depth

For example, a garden bed 4 meters long and 1.2 meters wide, with compost applied 10 cm (0.1 m) deep:

• Area = 4 × 1.2 = 4.8 m²
• Volume = 4.8 × 0.1 = 0.48 m³

When you're working with mixed units — say, a length in feet and a depth in inches — the calculator handles all unit conversions automatically. Just select the correct unit from the dropdown beside each input.

How deep you need to apply compost depends entirely on what you're trying to achieve. Here's a practical reference:

As a starting point for most established garden beds, 2–4 cm (roughly 1–1.5 inches) is a reliable standard. If you're improving genuinely poor or depleted soil, go deeper.

Once the calculator has your volume, the cost section does the arithmetic. Enter the price your supplier quotes per unit — most bulk compost is priced per cubic meter or cubic yard — and your total spend appears based on the actual volume you need.

A few things worth factoring into your budget:

• Bulk vs. bagged: Bulk compost delivered loose is typically 30–50% cheaper per cubic meter than the same material in bags. For volumes above 1 m³, bulk delivery almost always makes financial sense.
• Delivery charges: Large orders often include delivery; smaller orders may carry a flat delivery fee that adds meaningfully to the per-m³ cost.
• Compost grade: Screened, certified organic, or specialist composts carry a 20–40% price premium over standard product. The quality difference is often worth it for vegetable gardens.

For larger projects, get two or three quotes, then plug each price into the calculator to compare total costs instantly.

Weight matters more than most people anticipate when ordering compost. A 5 m³ order — which doesn't sound enormous — can easily weigh 3,000–4,000 kg. That's three to four tonnes arriving on one truck, which may be too heavy for a soft or sloping driveway, or impossible to position close to where you actually need it.

The weight calculation uses:

Total Weight = Volume × Density

Compost density varies significantly with moisture content and material type:

The calculator defaults to 650 kg/m³, a reasonable midpoint for typical mature compost. If accurate weight is important — rooftop gardens, balconies, or soft-ground access — ask your supplier for the actual bulk density of the product they're delivering.

Example 1: Two raised vegetable beds Two beds, each 2.4 m × 1.2 m, needing a 10 cm compost top-up:

• Area per bed: 2.4 × 1.2 = 2.88 m²; total area: 5.76 m²
• Volume: 5.76 × 0.1 = 0.58 m³
• At $180/m³: total cost = ~$104
• At 650 kg/m³: total weight = ~377 kg — manageable for a standard bagged or small bulk delivery

Example 2: Lawn top dressing A lawn 15 m × 10 m receiving a 1 cm (0.01 m) top dressing:

• Area: 150 m²; Volume: 150 × 0.01 = 1.5 m³
• At $150/m³: total cost = $225
• At 700 kg/m³: total weight = 1,050 kg — approximately 1 tonne, the typical minimum for a bulk delivery

Example 3: Large landscaping project A commercial planting area 30 m × 20 m with compost incorporated to 8 cm (0.08 m):

• Area: 600 m²; Volume: 600 × 0.08 = 48 m³
• At $120/m³ (bulk rate): total cost = $5,760
• At 650 kg/m³: total weight = 31,200 kg — multiple deliveries will be needed; confirm site access with your supplier

• Measure twice: A 5 cm difference in depth across a 100 m² area means an extra 0.5 m³ of material — roughly $75–150 in additional cost. Precise measurements pay off.
• Account for settling: Compost in raised beds can compress by 10–20% over the first season. Ordering slightly more than calculated is sensible for new installations.
• Ask for the actual density: If weight affects your project — rooftop gardens, structural requirements, or challenging site access — ask your supplier for the bulk density of the specific product rather than using an estimate.
• Compare bulk vs. bagged: For any project over 0.5 m³, enter the bulk price and the per-bag equivalent price into the cost section to compare total spend side by side.
• Add a 5–10% buffer for uneven ground: Irregular or sloped areas naturally use slightly more material than a flat calculation suggests. A small buffer helps ensure full coverage.