How to Calculate Cubic Metres of Soil

This guide shows you how to work out the volume of soil you need for a garden bed, planter, or landscaping project in cubic metres (m³). You enter the length, width, and depth of the space, and the calculation gives you the exact amount of soil to order. You’ll need a tape measure or measuring wheel, and a calculator (or the one below).

Formula

The volume of soil is calculated using the formula for a rectangular prism:

Volume (m³) = Length (m) × Width (m) × Depth (m)

Where:

• Length – the longest side of the area, in metres (m).
• Width – the shorter side of the area, in metres (m).
• Depth – how deep you want the soil, in metres (m). Since depth is often given in centimetres, convert it by dividing by 100 (e.g., 30 cm = 0.3 m).

If your area is not a perfect rectangle, break it into smaller rectangles, calculate each one, and add them together.

Worked Example

Using the default values from the calculator above:

• Length = 2 m
• Width = 1 m
• Depth = 30 cm = 0.3 m

Step 1: Convert depth to metres: 30 cm ÷ 100 = 0.3 m

Step 2: Multiply length × width × depth: 2 × 1 × 0.3 = 0.6

So you need 0.6 cubic metres of soil. That matches the calculator’s output.

When to Use This Calculation

Use this whenever you’re filling a raised garden bed, a planter box, a new lawn area, or a flower bed. It also helps when ordering topsoil, compost, or fill dirt from a supplier, as they usually sell by the cubic metre. Knowing the volume lets you compare prices and avoid over-ordering or running short.

How to Read the Result

The result is the total volume of soil needed, expressed in cubic metres (m³). One cubic metre is a cube that is 1 metre on each side – roughly the size of a standard washing machine. If you’re ordering soil in bags, note that bags are often sold in litres (L). There are 1,000 litres in a cubic metre, so multiply the cubic metres by 1,000 to get litres. For example, 0.6 m³ = 600 litres.

Common Mistakes

• Mixing units: Forgetting to convert centimetres to metres before multiplying. Always use the same unit (metres) for all three dimensions.
• Measuring the wrong area: For a raised bed, measure the inside dimensions, not the outside. For a sloped area, measure the actual surface, not the horizontal projection.
• Ignoring compaction: Soil settles after watering and time. If you’re filling a bed that will be planted immediately, you may need 10–20% extra to account for settling.
• Rounding too early: If you round each dimension to the nearest whole number, you can over- or under-estimate significantly. Keep at least one decimal place during calculations.

Tips

• Measure in metres and centimetres for accuracy. If your tape measure shows feet and inches, convert: 1 foot = 0.3048 m, 1 inch = 0.0254 m.
• For irregular shapes, divide the area into rectangles. For a triangular corner, use (length × width × depth) ÷ 2.
• When ordering, add 5–10% extra to account for spillage and uneven settling, especially for large projects.
• If you’re filling a raised bed that already has some soil, measure the depth of the empty space, not the full height of the bed.
• Use the calculator above to double-check your manual math – it’s easy to make a slip when multiplying decimals.

Troubleshooting

My result seems too large or too small. Re-check your measurements. A common error is measuring in feet but treating the number as metres. For example, a bed that is 4 ft × 2 ft × 1 ft is about 0.23 m³, not 8 m³.

The area is not a perfect rectangle. Break it into smaller rectangles, calculate each, and add the volumes. If it’s a circle, use the formula for a cylinder: π × radius² × depth (with radius in metres).

I measured in centimetres but the calculator expects metres. The calculator above accepts depth in centimetres, but length and width must be in metres. If your length is 200 cm, enter 2 m.

I need soil for a sloped area. Measure the depth at the deepest point and the shallowest point, average them, and use that average depth in the calculation.

Frequently Asked Questions

How many bags of soil do I need for 1 cubic metre?

That depends on bag size. A typical bag holds 25–50 litres. One cubic metre equals 1,000 litres, so you’d need 20–40 bags. Check the bag label for volume.

How deep should soil be for a vegetable garden?

Most vegetables need at least 15–20 cm of good soil. Root vegetables like carrots need 30–45 cm. For raised beds, 30 cm is a common minimum.

Should I order more soil than the calculation shows?

Yes, it’s wise to add 5–10% extra to cover settling, compaction, and spillage. For loose, fluffy soil, add up to 20%.

How do I convert cubic metres to cubic feet?

Multiply the cubic metres by 35.3147. For example, 0.6 m³ × 35.3147 = 21.19 cubic feet.

Can I use this formula for circular planters?

For a circular planter, use the formula: π × (radius in m)² × depth in m. The radius is half the diameter. For example, a planter 1 m wide and 0.5 m deep: π × 0.5² × 0.5 ≈ 0.39 m³.

What if my measurements are in feet and inches?

Convert everything to metres first. 1 foot = 0.3048 m, 1 inch = 0.0254 m. Then use the formula. For a quick estimate, 1 cubic yard ≈ 0.7646 m³.

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in l | Length | m | 2 | 0
in w | Width | m | 1 | 0
in d | Depth | cm | 30 | 0
out vol | Soil volume | m³ | l * w * (d / 100) | 2