Quick Answer: Multiply Length (ft) x Width (ft) x Depth (in) / 12 to get cubic feet of soil. A 4x8 ft bed at 12 inches deep needs 32 cu ft (1.19 cu yd). That is 32 bags of 1 cu ft soil or 16 bags of 2 cu ft soil. A 4x4 bed needs 16 cu ft (0.59 cu yd). Add 10% for settling. Soil costs $3-8 per bag or $30-50 per cubic yard bulk.
Calculate exactly how much soil you need to fill your raised garden beds. Select a preset bed size or enter custom dimensions, choose your soil mix, and get the results in both cubic feet (for buying bags) and cubic yards (for bulk delivery).
How to Calculate Soil for Raised Beds
The formula for raised bed soil volume:
- Measure the inside length and width of your bed frame in feet.
- Decide on soil depth: 10-12 inches for most vegetables, 6-8 for herbs, 12-18 for root crops.
- Multiply length × width × depth (converted to feet) to get cubic feet.
- For bags: 1 cu ft bags = total cubic feet, 2 cu ft bags = total ÷ 2.
- For bulk: divide cubic feet by 27 to get cubic yards.
- Add 10% for settling and compaction after watering.
Soil Needed for Common Bed Sizes
Quick reference for popular raised bed sizes at 12 inches deep (includes 10% for settling):
| Bed Size | Cubic Feet | Cubic Yards | Bags (2 cu ft) |
|---|---|---|---|
| 2 x 8 ft | 17.6 | 0.65 | 9 |
| 3 x 6 ft | 19.8 | 0.73 | 10 |
| 4 x 4 ft | 17.6 | 0.65 | 9 |
| 4 x 8 ft | 35.2 | 1.30 | 18 |
| 4 x 12 ft | 52.8 | 1.96 | 27 |
Best Soil Mixes for Raised Beds
- Mel's Mix (1/3-1/3-1/3): Equal parts compost, peat moss (or coconut coir), and coarse vermiculite. Created by the Square Foot Gardening method. Excellent drainage, lightweight, and nutrient-rich. Best for intensive vegetable gardening.
- Raised Bed Mix: Pre-blended soil from landscape suppliers, typically topsoil with compost and perlite or bark fines. A good all-purpose option that balances cost and quality. Weighs about 1,700 lbs per cubic yard.
- Garden Mix (60/40): 60% screened topsoil and 40% compost. More affordable than specialty mixes. Works well for most vegetables and flowers. Heavier at 1,800 lbs per cubic yard. May compact over time.
- Compost Blend (50/50): Half compost, half topsoil. Very rich in nutrients and organic matter. Best mixed with perlite or sand to improve drainage. Lightweight at 1,600 lbs per cubic yard.
- Plain Topsoil: The most affordable option but needs amendments. Mix in compost (30-40% by volume) and perlite before filling beds. Dense at 2,200 lbs per cubic yard and may drain poorly without amendments.
Bags vs. Bulk: Which Is Cheaper?
The cost difference between bags and bulk delivery is significant for larger projects:
| Method | Cost per Cu Yd | Best For |
|---|---|---|
| 1 cu ft bags ($3-6 each) | $80-160 | 1 small bed |
| 2 cu ft bags ($5-10 each) | $70-135 | 1-2 beds |
| Bulk delivery | $30-50 | 3+ beds |
For a single 4x8 bed (1.3 cu yd), bags cost roughly $100-200 while bulk delivery would be $40-65 plus a $50-100 delivery fee. The break-even point is typically around 2-3 cubic yards (two to three 4x8 beds).
Tips for Filling Raised Beds
- Line the bottom: Place cardboard or landscape fabric at the bottom to suppress weeds growing up from below. Cardboard decomposes within a season; fabric lasts longer but prevents worm migration.
- Use the hugelkultur technique: For beds taller than 12 inches, fill the bottom third with logs, branches, and yard waste. This reduces the soil needed by 30-40% and the decomposing wood releases nutrients and retains moisture.
- Water as you fill: Add soil in 4-inch layers and water each layer before adding the next. This eliminates air pockets and helps the soil settle evenly.
- Overfill slightly: Fill beds 1-2 inches above the rim. New soil settles 10-20% over the first season from watering and decomposition.
- Plan for annual topping: Budget for 1-2 inches of compost each spring to replace what decomposes and settles. This maintains soil volume and adds fresh nutrients.
Formula Summary
Raised Bed Soil Volume: Volume (cu ft) = Length (ft) × Width (ft) × Depth (in) / 12.
V(cu ft) = L(ft) × W(ft) × D(in) / 12
Multiple Beds: Total = V(cu ft per bed) × Number of Beds × (1 + W%).
Bags: 1 cu ft bags = ⌈Total cu ft⌉. 2 cu ft bags = ⌈Total cu ft / 2⌉.
| Soil Mix | Density (lbs/cu yd) |
|---|---|
| Topsoil | 2,200 |
| Garden Mix | 1,800 |
| Compost Blend | 1,600 |
| Raised Bed Mix | 1,700 |
| Mel's Mix | 1,400 |
Standard Assumptions: 10% waste factor for settling and compaction. 1 cubic yard = 27 cubic feet. Common bed depth is 12 inches. Preset sizes: 4x4, 4x8, 3x6, 2x8, 4x12 feet.
Related Calculators
- Topsoil Calculator — calculate topsoil for lawns and garden beds
- Mulch Calculator — estimate mulch for garden beds and pathways
- Cubic Yard Calculator — convert any dimensions to cubic yards
- Gravel Calculator — calculate gravel for raised bed drainage layers
Estimates are for planning purposes only. Consult a qualified contractor for critical projects. Actual material requirements may vary based on site conditions, waste, and installation methods.
Pricing last verified: February 2026. Material prices vary by region, season, and supplier. Prices shown are national averages for planning purposes.