🌍 Soil Calculators

Calculate soil volume, raised bed fill, topsoil, compost, and mulch quantities for your garden projects.

All Soil Tools

Soil Volume Calculator Calculate the volume of soil needed for garden beds, pots, and planting areas based on dimensions. Raised Bed Calculator Calculate how much soil, compost, and amendments you need to fill a raised garden bed of any size. Topsoil Calculator Calculate how many cubic yards or tons of topsoil you need to cover a lawn or garden area. Compost Calculator Calculate how much compost to add to your garden based on area size and recommended application depth. Mulch Calculator Calculate how many cubic yards or bags of mulch you need to cover garden beds at the recommended depth.

Calculating Soil Volume for Garden Beds

Soil volume for a rectangular raised bed is simply length Γ— width Γ— depth. A 4 ft Γ— 8 ft bed filled to 12 inches deep requires 4 Γ— 8 Γ— 1 = 32 cubic feet, or about 1.19 cubic yards. Soil is sold by the cubic yard (for bulk delivery) or cubic foot (for bagged soil). One cubic yard equals 27 cubic feet. A standard 40-litre bag of potting mix contains about 1.4 cubic feet. For circular beds, volume = Ο€ Γ— radiusΒ² Γ— depth. Always add 10–15% extra to account for settling β€” fresh loose soil compresses as it absorbs water and organic matter decomposes over the first growing season.

Topsoil vs. Garden Soil vs. Potting Mix

Topsoil is the upper 5–20 cm of native soil, often sold in bulk. It varies enormously in quality but provides a good base layer for raised beds. Garden soil is a blended product designed for in-ground planting; it contains topsoil plus amendments and is not suitable for containers because it compacts too densely. Potting mix is a soilless blend of peat or coco coir, perlite, and compost, designed for containers and raised beds. It drains well, resists compaction, and is lightweight. A common raised bed fill recipe is the Mel's Mix from the Square Foot Gardening method: 1/3 blended compost, 1/3 peat moss or coco coir, and 1/3 coarse vermiculite.

Compost and Mulch Applications

Compost improves soil structure, adds nutrients, and supports beneficial microbial activity. A standard application rate for garden beds is 2–4 inches (5–10 cm) incorporated into the top 6–8 inches of soil, or a 1-inch top-dressing applied annually. For a 100 square foot bed: 2 inches of compost = 100 Γ— (2/12) β‰ˆ 16.7 cubic feet β‰ˆ 0.62 cubic yards. Mulch is applied on top of soil to suppress weeds, retain moisture, and regulate soil temperature. Standard mulch depth is 2–4 inches; too deep (over 4 inches) can suffocate plant roots and create habitat for pests. Organic mulches (wood chips, straw, shredded leaves) decompose over 1–3 years and improve soil structure as they break down.

Soil pH and Nutrient Availability

Soil pH affects the availability of nearly all plant nutrients. Most vegetables grow best in soil with pH 6.0–7.0 (slightly acidic to neutral). At pH below 5.5, phosphorus, calcium, and magnesium become less available; aluminium and manganese can reach toxic levels. At pH above 7.5, iron, manganese, boron, and zinc become deficient. To raise pH (acidic soil), add garden lime (calcium carbonate) β€” typically 5–10 lb per 100 square feet to raise pH by 1 unit. To lower pH (alkaline soil), add elemental sulphur β€” approximately 1–2 lb per 100 square feet to lower pH by 0.5 units, though effects take 3–6 months. A soil test from your local extension service provides pH, nutrient levels, and specific amendment recommendations.