Soil & Compost Volume Guide
Working out how much soil or compost you need for raised beds, planters, and borders is one of the most common gardening calculations. This guide covers standard raised bed volumes, the bag sizes available from UK garden centres, and the conversions you'll need to order the right amount.
Raised Bed Volumes by Size
| Bed Size (ft) | Bed Size (m) | Depth | Volume (litres) | Volume (m³) |
|---|---|---|---|---|
| 3 × 3 | 0.9 × 0.9 | 30 cm | 243 | 0.24 |
| 4 × 4 | 1.2 × 1.2 | 30 cm | 432 | 0.43 |
| 4 × 8 | 1.2 × 2.4 | 30 cm | 864 | 0.86 |
| 4 × 8 | 1.2 × 2.4 | 45 cm | 1,296 | 1.30 |
| 4 × 10 | 1.2 × 3.0 | 30 cm | 1,080 | 1.08 |
| 6 × 6 | 1.8 × 1.8 | 30 cm | 972 | 0.97 |
| 6 × 8 | 1.8 × 2.4 | 30 cm | 1,296 | 1.30 |
| 8 × 8 | 2.4 × 2.4 | 30 cm | 1,728 | 1.73 |
Volumes assume the bed is filled to the top. In practice, soil settles by 10–15% over the first few months, so order a little extra.
UK Compost & Soil Bag Sizes
| Bag Size | Volume (litres) | Approx. Weight | Best For |
|---|---|---|---|
| Small bag | 10–20 L | 5–10 kg | Pots, window boxes, small top-ups |
| Standard bag | 40 L | 15–20 kg | Most common; containers, small beds |
| Large bag | 50–60 L | 20–25 kg | Larger planters, bed top-ups |
| Extra large bag | 100 L | 35–45 kg | Raised beds, borders |
| Bulk bag (dumpy bag) | ~850 L (0.85 m³) | ~500–750 kg | Large projects, multiple beds |
| Loose load (per m³) | 1,000 L | ~800–1,100 kg | Very large gardens, allotments |
Quick Volume Conversions
1 cubic metre (m³) = 1,000 litres. A standard bulk bag is roughly 0.85 m³, so you need just over one bulk bag per cubic metre. To convert litres to cubic metres, divide by 1,000. For example, 500 litres = 0.5 m³.
Calculate Exactly What You Need
For precise quantities tailored to your exact bed dimensions, use our free calculators:
- Soil & Compost Calculators — raised bed fill calculator, compost quantity estimator and more
Bag weights vary depending on moisture content and the specific product. Bulk bag volumes are approximate and depend on how the bag is filled. Always order 10–15% extra to account for settling.