Free garden soil calculator: how much soil a raised bed needs in cubic yards, bags, mix ratios, weight and cost.
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Choose imperial or metric units and the bed shape. For a rectangular bed enter length, width and soil depth; for a round bed enter the diameter and depth. Set how many identical beds you have and pick a settling buffer (10% is the safe default, since fresh soil settles after the first waterings). The calculator instantly shows the soil volume in cubic feet, cubic yards, cubic metres and litres, how many bags that is in common bag sizes, the 60/30/10 mix split, the estimated weight in tons and the number of wheelbarrow loads.
Soil volume is length × width × depth, with depth converted to the same units. A 4 ft × 8 ft bed at 12 inches deep is 4 × 8 × 1 = 32 cubic feet, or 32 / 27 = 1.19 cubic yards. For round beds it is pi × radius squared × depth: a 4 ft diameter bed at 12 inches is pi × 4 × 1 = 12.57 cubic feet. Metric users get cubic metres directly: a 1.2 m × 2.4 m bed at 30 cm is 0.864 cubic metres, or 864 litres. The quick mental shortcut gardeners use is (square feet × depth in inches) / 324 for cubic yards.
Select imperial or metric, then rectangle or circle. Measure the INSIDE dimensions of your bed, because the timber or metal walls eat several inches on each side, and enter the depth you actually want to fill, not the height of the frame. Set the number of identical beds if you are filling several at once, and leave the settling buffer at 10% unless you like buying soil twice. All results update live, including bag counts, the mix split, weight and wheelbarrow loads.
The classic 4 ft × 8 ft raised bed at 12 inches deep needs 32 cubic feet, which is 1.19 cubic yards. That is 22 bags of 1.5 cubic feet, or 16 bags of 2 cubic feet. With the 10% settling buffer it becomes 35.2 cubic feet, or 24 bags of 1.5 cubic feet. At 6 inches deep, halve everything: 16 cubic feet, or 11 bags. This is the single most-asked soil question on the internet, and the reason most gardeners under-buy on their first trip.
Depth decides the volume more than anything else. Salad greens and herbs do fine in 6 to 8 inches. Most vegetables need 10 to 12 inches. Root crops like carrots and deep-rooted plants want 18 to 24 inches. Deeper than 18 inches gets expensive fast, so many gardeners fill the bottom with logs, branches and leaves (the hugelkultur method) and put only the top 12 inches of purchased soil on top.
The classic recipe is 60% topsoil, 30% compost and 10% aeration material like perlite or coarse sand. Mel's Mix is an even simpler 1:1:1 blend of compost, peat moss and coarse vermiculite. Budget gardeners use a 50/50 mix of topsoil and compost and top-dress every year. Never fill a raised bed with pure compost (it shrinks and drains too fast) or pure garden soil (it compacts and drains poorly). The calculator splits your total into the 60/30/10 components automatically.
One cubic yard is 27 cubic feet, so it takes 18 bags of 1.5 cubic feet, 14 bags of 2 cubic feet, or 36 bags of 0.75 cubic feet to equal a yard. In metric, a cubic metre is 1,000 litres, so 20 bags of 50 litres or 40 bags of 25 litres. Bagged soil is sold by loose volume, so it compresses in the bag; bulk soil is measured loose, which is one more reason to add the settling buffer.
Topsoil is the mineral base, garden soil is topsoil blended with organic matter, compost is decomposed organic matter that feeds plants, fill dirt is subsoil for grading (no nutrients), and potting mix is a light soilless blend for containers. Do not fill raised beds with cheap garden soil straight from the bag and call it done; it is designed to be mixed, not used alone. Compost does the nutritional heavy lifting in any mix.
Yes. Freshly filled soil settles 10 to 15% after the first few waterings and the first season. Either buy 10% extra up front, which this calculator does with the settling buffer, or plan a top-up of 2 to 4 inches of fresh mix each spring. Skipping this is why beds that looked full in April are half-empty by July.
Bagged soil wins for small projects: it is clean, consistent and easy to carry. Bulk soil by the cubic yard wins once you pass roughly 15 to 18 bags, because the per-yard price is far lower than retail bags. The break-even point is usually around 1 to 2 cubic yards. A cubic yard of dry topsoil weighs roughly 2,000 lb (one ton), so check your truck's payload and plan wheelbarrow trips before ordering bulk.
Topsoil weighs about 75 lb per cubic foot (around 2,000 lb per cubic yard dry), compost about 40 lb per cubic foot, potting mix about 30 lb. Wet soil can be 20 to 50% heavier, so a 4x8 bed's worth of topsoil is roughly 1.2 tons dry. A standard wheelbarrow holds about 3 cubic feet, so the 32 cubic feet of a 4x8 bed is 11 to 12 loads. The calculator shows the weight and the wheelbarrow count so you can plan the delivery and the workout.
The five classics: measuring the outside of the bed instead of the inside, filling with pure compost, filling with pure garden soil, forgetting the settling buffer, and filling a very deep bed entirely with purchased soil instead of hugelkultur filler at the bottom. Small windows of correction exist for all of them, but measuring twice and ordering once is cheaper. You can also reuse last year's potting soil: refresh it with one part fresh compost to three parts old mix, except after diseased crops.
Multiply length × width × depth. A 4x8 ft bed at 12 inches deep needs 32 cubic feet, or 1.19 cubic yards, plus about 10% extra for settling. Enter your bed's inside dimensions in the calculator for the exact volume, bag count, mix split and weight.
At 12 inches deep with the 10% settling buffer, 24 bags of 1.5 cubic feet, or 18 bags of 2 cubic feet. In metric, a 1.2x2.4 m bed at 30 cm needs 18 bags of 50 litres. Bag sizes vary by brand, so the calculator shows several sizes at once.
A cubic yard is 27 cubic feet, which equals 18 bags of 1.5 cubic feet, 14 bags of 2 cubic feet, or 36 bags of 0.75 cubic feet. Bulk soil is sold loose by the yard, so buying 18 bags is roughly the break-even point with bulk delivery.
6 to 8 inches for herbs and greens, 10 to 12 inches for most vegetables, 18 to 24 inches for root crops and deep-rooted plants. Deeper beds cost much more to fill, so use logs and leaves as filler at the bottom of very deep beds.
The classic mix is 60% topsoil, 30% compost and 10% aeration material like perlite. Mel's Mix is a 1:1:1 blend of compost, peat moss and vermiculite. Avoid filling a bed with pure compost or pure garden soil; both fail on their own.
Topsoil is the mineral base layer, while garden soil is topsoil pre-blended with organic matter. Neither is complete on its own for raised beds; both need compost mixed in. Compost is decomposed organic matter that feeds plants, and fill dirt is nutrient-free subsoil for grading.
Dry topsoil weighs roughly 2,000 lb (one ton) per cubic yard. Compost is lighter at about 1,000 to 1,400 lb per yard, and wet soil can be 20 to 50% heavier. Check your vehicle's payload before picking up bulk soil.
Not straight from the bag. Garden soil compacts and drains poorly when used alone. Mix it at least half-and-half with compost, or use the 60/30/10 recipe (topsoil, compost, aeration). Pure garden soil is the most common reason for sad first-year beds.
Yes, add 10 to 15% extra, or plan an annual top-up of 2 to 4 inches. Fresh soil settles after the first waterings, and beds that looked full in spring sit noticeably lower by midsummer. The calculator's settling buffer handles this automatically.
Around 1 to 2 cubic yards, or roughly 15 to 18 standard bags. Below that, bagged soil is cheaper and easier; above it, bulk delivery per yard costs far less. Factor in delivery fees and the physical work of moving a ton of soil.
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