Raised-bed soil volume should be calculated from the internal area and the depth you actually intend to fill. The outside height of the bed is not automatically the required soil depth.
Use consistent units
For a rectangular space, multiply internal length by width by fill depth in metres to obtain cubic metres. Multiply that result by 1,000 for litres. An internal bed measuring 1.2 × 0.6 m filled to 0.3 m requires a geometric volume of 0.216 m³, or 216 L.
| Shape | Basic calculation |
|---|---|
| Rectangle | Length × width × fill depth |
| Circle | 3.1416 × radius × radius × fill depth |
| Irregular shape | Divide into simpler sections and add their volumes |
Adjust the estimate for the actual bed
Account for any internal structures and the intended unfilled space at the top. Soil can settle, and bagged volume is not a guarantee of the final settled level. Use the calculation as a purchasing estimate and follow appropriate planting and soil guidance for the chosen plants. Do not assume every crop needs the full wall height filled with the same material. Consider drainage, the surface beneath the bed and the load, especially on a balcony or raised structure. Confirm support and site suitability before bringing in a large quantity of soil.
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Raised garden beds, Plant Pots & Planters.