Raised Garden Bed Calculator
Calculate the soil, compost, and lumber needed for a raised garden bed. Get exact quantities for any size bed using the Mel's Mix formula (1/3 compost, 1/3 peat moss, 1/3 vermiculite) or topsoil blend.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Raised Garden Bed Calculator | Volume = Length x Width x Height / 27 (cubic yards) | cu ft of soil mix |
Step-by-Step Examples
4x8 ft bed, 12 inches high, Mel's Mix.
- Volume = 4x8x1 = 32 cu ft
- Compost: 10.7 cu ft | Peat: 10.7 cu ft | Vermiculite: 10.7 cu ft
- Buy in 2 cu ft bags: 5-6 bags each component
Three 4x4 ft beds, 10-inch height, topsoil blend.
- Volume per bed = 4x4x(10/12) = 13.3 cu ft
- Total = 13.3 x 3 = 40 cu ft
- Topsoil: 20 cu ft | Compost: 20 cu ft = 0.74 cu yds each
4x8 ft, 24-inch deep (for carrots/parsnips).
- Volume = 4x8x2 = 64 cu ft = 2.37 cu yds
- Compost: 21.3 cu ft | Peat: 21.3 | Vermiculite: 21.3
- Deeper beds suit root vegetables and small trees
Real-World Applications
Common Mistakes to Avoid
New raised beds almost always need more soil than calculated because purchased topsoil and compost settle 15-20% over time. Buy 10-15% extra or be prepared to top off after the first season.
Pure topsoil in raised beds compacts over time and drains poorly. Always amend with at least 30-50% compost for proper drainage, aeration, and nutrition.
Standard width is 3-4 feet max so you can reach the center without stepping in. Stepping in raised beds compacts soil, undoing the drainage and aeration benefits.