This garden soil calculator tells you exactly how much soil to buy for a raised bed or garden plot — in cubic feet, cubic yards for bulk delivery, and the bag count for the garden-center run — with a classic 60/30/10 blend breakdown.
Length × Width × Depth — Then the Bag Math
Volume in cubic feet = L × W × (depth in inches ÷ 12). Divide by 27 for cubic yards (the bulk-delivery unit) and by bag size for the retail count — the two conversions every raised-bed project dies without. Topping beds with mulch instead? Our Mulch Calculator. Part of our Ecology Calculators collection.
Worked Example (Verified)
- Standard 8 × 4 ft bed, 12 in deep (defaults): 8 × 4 × 1 = 32 cu ft = 1.19 cu yd → 22 bags of 1.5 cu ft or 16 bags of 2 cu ft
- Blend at that volume: 19.2 cu ft topsoil + 9.6 compost + 3.2 aeration — the 60/30/10 that most extension services teach
- Four beds: 128 cu ft ≈ 4.7 cu yd — unambiguously bulk-delivery territory; bagging it would be ~86 bags and a chiropractor appointment
- Depth reality check: 12 in suits most vegetables; 6–8 in suffices for shallow greens and herbs; 18 in+ for root crops and for gardeners who’d rather not bend — soil math follows the carpentry
Buying & Filling Wisdom
- Hugelkultur-style filling (logs/branches in the bottom third of deep beds) cuts purchased volume substantially — subtract that fill from your depth before calculating.
- “Topsoil” quality varies from screened loam to construction fill with ambitions — for vegetable beds, the compost fraction is where the life is; don’t economize there.
- Wet soil weighs ~2,000+ lb per cubic yard delivered damp; plan the wheelbarrow route and the delivery drop point accordingly.
- Top up annually: beds lose an inch or two a year to decomposition — that’s not failure, it’s the soil food web eating.
Related Tools
- Mulch Calculator — the layer that goes on top
- Compost Calculator — brewing the 30% fraction yourself
- Ecology Calculators — the full collection
Frequently Asked Questions
How much soil does an 8×4 raised bed need?
At 12 inches deep: 32 cubic feet (1.19 cubic yards) — that’s 22 bags of 1.5 cu ft or 16 bags of 2 cu ft. At 8 inches deep, two-thirds of that (~21 cu ft). This calculator does the volume and both bag counts for any dimensions.
How many bags of soil in a cubic yard?
27 cubic feet per cubic yard: eighteen 1.5 cu ft bags or thirteen-and-a-half 2 cu ft bags. The crossover where bulk delivery gets cheaper usually sits right around one cubic yard, depending on local bag prices and delivery fees.
What is the best soil mix for raised beds?
The widely taught baseline is 60% topsoil, 30% compost, 10% aeration material (perlite, vermiculite or coir). Square-foot gardeners use “Mel’s Mix” (thirds of compost, peat/coir and vermiculite) — richer and pricier. Either way, compost quality drives results more than the exact ratio.
How deep should raised bed soil be?
6–8 inches grows greens and herbs; 10–12 inches covers most vegetables; 18 inches+ suits root crops, poor underlying ground, and sit-to-garden ergonomics. Remember roots also exploit the soil beneath an open-bottom bed — depth buys insurance, not permission.
Why did my new bed’s soil level drop?
Settling and decomposition: fluffy bagged soil compacts 10–20% in year one, and the organic fraction is literally being eaten into plant food and CO₂. Top up with compost each season — the calculator’s volume plus an extra ~10% pre-empts the surprise.
Is this garden soil calculator free?
Yes — free, instant, no sign-up.