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Plan soil or compost quantities for raised beds and planting areas.
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Soil calculator guide
A soil calculator turns the length, width, and depth of a planting area into a volume of soil or compost to order. It is useful for raised beds, garden borders, planters, lawn top-dressing, and filling an excavated area. The calculation converts the entered depth from inches to feet, multiplies the dimensions to find cubic feet, applies the waste allowance, and converts the result to cubic yards, with cubic feet and cubic meters shown alongside. Bulk soil is usually sold by the cubic yard or by the bag, and bagged products list their volume in cubic feet or liters, so having the figure in several units saves a conversion at the garden center. Soil settles by roughly a tenth of its loose depth after watering, beds may have uneven bases, and bag sizes vary, so use the result as a purchase estimate rather than an exact promise of finished height.
Base volume (ft³) = length (ft) × width (ft) × depth (in) ÷ 12. Adjusted volume (yd³) = base volume (ft³) × (1 + waste ÷ 100) ÷ 27. Cubic meters = adjusted volume (ft³) × 0.0283168.
Worked example with the default raised bed: 12 ft long, 4 ft wide, and filled 12 in deep. The depth converts to 12 ÷ 12 = 1 ft, so the base volume is 12 × 4 × 1 = 48 ft³, or 48 ÷ 27 = 1.78 yd³ before any allowance. The default 10% allowance for settling and uneven fill gives 48 × 1.10 = 52.8 ft³, and 52.8 ÷ 27 = 1.96 yd³, which is the recommended quantity the calculator displays. The metric row shows 52.8 × 0.0283168 = 1.5 m³. If your supplier sells 2 ft³ bags, 52.8 ÷ 2 = 26.4, so buy 27 bags.
Enter length and width in feet and depth in inches. One foot of depth equals 12 inches, and one cubic yard equals 27 cubic feet. Keep the waste allowance as a percentage such as 10 for 10%. Bagged soil is often labeled in cubic feet (typically 1, 1.5, or 2 ft³) or in liters; 1 ft³ is about 28.3 liters, so a 50 L bag is roughly 1.77 ft³.
The result estimates the amount to buy before settling and compaction. Soil type, moisture, delivery volume, and the final level of the bed can change the practical quantity. The 80 lb bag row comes from the shared volume engine and applies to concrete mix, not soil; use your product’s bag volume instead.
Do not confuse bed depth with the surface area: a 12 × 4 ft bed has 48 square feet of surface regardless of depth, but every extra inch of depth adds 4 more cubic feet. Do not mix inches and feet without converting, and do not order by bag count without checking each product’s stated volume, because a “large” bag can hold anywhere from 1 to 3 cubic feet. Subtract any gravel drainage layer or the volume of a hügelkultur log base before ordering, and remember that compost mixed into existing ground needs only the top few inches, not the full bed depth.
Confirm soil blend, bag yield, settling allowance, drainage layer, and delivery minimums with the supplier or garden professional.
Sources
How it works
Plan soil or compost quantities for raised beds and planting areas. This tool explains the calculation so you can adjust the assumptions to match your situation.
Worked example
With Length = 12 ft · Width = 4 ft · Depth = 12 in · Waste allowance = 10 % → 1.96 yd³ (recommended slab volume including waste). Change an input above and this example updates with your numbers.
Common questions
Multiply the bed length by width and depth in feet to get cubic feet, divide by 27 for cubic yards, and add a modest allowance for settling and uneven fill. A 12 × 4 ft bed filled 12 inches deep needs about 1.96 cubic yards with a 10% allowance.
The base volume is 12 × 4 × 1 = 48 cubic feet, or about 1.78 cubic yards. With the default 10% allowance, plan for 52.8 cubic feet, which is about 1.96 cubic yards or roughly 27 two-cubic-foot bags.
Multiply cubic yards by 27 to get cubic feet, then divide by the volume printed on one bag and round up. Bag sizes and fill volumes vary from about 1 to 3 cubic feet, so always use the product label rather than a generic figure.
Usually a 10% allowance is sensible, because loose soil settles once watered and compacts under planting. The right amount depends on soil blend, moisture, compaction, and whether the bed will be topped up later with compost each season.
No. Measure the soil-filled portion separately from gravel, edging, or other layers that do not contain soil. If a 12-inch bed has 3 inches of gravel at the bottom, enter 9 inches as the soil depth.