Soil Calculator

Every soil calculator — whether for a raised bed, a garden border, or a large lawn area — starts with the same idea: volume equals area multiplied by depth. In imperial units the depth is usually measured in inches while the length and width are in feet, so a single conversion step is required.

Worked example. A rectangular raised bed that is 3 ft wide by 6 ft long, filled to a depth of 10 inches:

Depth is the most critical variable. A difference of just 2 inches across a 4 × 8 ft bed changes the total by more than 5 cubic feet — enough to mean several extra bags. Always measure or plan depth carefully before purchasing.

A raised bed soil calculator applies the same length × width × depth formula, but the fill depth is the full interior depth of the bed rather than a thin surface layer. Enter each raised bed as a separate area in the calculator; if you have several beds of different sizes, add them one by one and the tool sums the totals automatically.

Common raised-bed examples at 1 ft (12 in) fill depth:

This soil calculator for raised beds also lets you add a settling allowance — for example +10% — so you buy a little extra to account for natural compaction after watering in. Selecting +10% on the 32 cu ft example above gives 35.2 cu ft, which rounds up to 47 bags of 0.75 cu ft.

For planning what to plant once the bed is filled, the Plant Spacing Calculator can help you lay out rows and spacing for your crop or flower arrangement.

Bagged soil is nearly always sold by the cubic foot in the United States, so the soil calculator cubic feet output is what you use at the garden center. Bulk soil delivered by truck is priced and quoted per cubic yard, making the soil calculator cubic yards reading more relevant for large projects.

The calculator displays both units simultaneously — cubic yards and cubic feet in imperial mode — so you can compare bulk vs. bagged pricing directly. If you are also adding mulch on top of the soil, the Mulch Calculator uses the same approach for mulch depth calculations on the same beds.

Switch the calculator to Metric mode and dimensions are entered in meters (m) with depth in centimeters (cm). The results panel then shows volume in cubic meters (m³) and liters, and bag sizes switch to liter options (20 L, 25 L, 40 L, 50 L, or custom).

Key metric conversion factors used by the soil calculator cm and soil calculator liters modes:

For reference, 1 cubic foot is approximately 28.32 liters; 1 cubic yard is approximately 764.6 liters (0.7646 m³). The British spelling "litres" also appears on some bag labels — they mean the same thing. The calculator's metric bag sizes align with common bag sizes sold in metric markets.

To find how many bags of soil you need, divide your total volume in cubic feet by the volume of one bag, then always round up — you cannot buy a fraction of a bag, and running short mid-project means a second trip.

Bag sizes vary widely — always check the label. Common sizes are 0.5, 0.75, 1.0, 1.5, and 2.0 cubic feet in the US. The soil calculator lets you select the exact bag size you plan to purchase, or enter a custom size.

Example — 4 × 8 raised bed at 1 ft depth (32 cu ft base, +10% settling = 35.2 cu ft):

The calculator's "Extra Material / Settling Allowance" option handles this automatically — select 0%, +5%, +10%, or +15%, or type a custom percentage. The results panel shows both the base bag count and the adjusted recommended count side by side.

The soil calculator for pots uses the Pot / Container shape option. Enter the pot's top opening diameter and the fill depth, and the calculator treats the container as a cylinder: π × (diameter ÷ 2)² × depth. The diameter can be entered in inches or feet independently of the global unit toggle, which is useful when shopping at a nursery where pots are labeled in inches but beds are planned in feet.

A common question is how much soil for a 5-gallon pot. A 5 US gallon container has an interior volume of roughly 0.67 cu ft (about 19 liters) at full capacity. In practice, pots are not filled all the way to the rim — a small gap is left for watering — so the actual soil needed will be somewhat less. Enter the diameter and your intended fill depth into the calculator to get a precise figure for your specific container.

If you are planning a container garden across multiple pot sizes, add each pot as a separate area using the "Add another area / pot" button. The results panel totals all areas and calculates one combined bag count and cost estimate.

Not every bed or planting area is a rectangle. The soil calculator circle mode accepts a diameter and depth; the soil calculator triangle mode takes a base, a perpendicular height, and a depth.

The triangle formula requires the perpendicular height — the straight-line distance from the base to the opposite vertex at a right angle, not the length of a slanted side. A labeled diagram appears inside the calculator when you select the Triangle shape to help clarify this.

If your garden has an irregular shape that doesn't fit neatly into one category, break it into simpler sub-sections, add each as a separate area, and the calculator totals them.

The appropriate depth depends heavily on what you are doing. A light topdressing of an existing lawn, filling a deep raised bed for root vegetables, and refreshing a container garden are very different tasks with very different depth requirements.

General considerations — not universal prescriptions. Consult plant guidance or local agricultural extension advice for your specific situation:

• Topdressing a lawn or existing bed: Thin applications are common, and depth varies from a light covering to a few inches depending on the condition of the existing surface.
• Raised beds: Depth depends on what is being grown. Shallow-rooted plants need less depth than deep-rooted crops. Check seed packets or local planting guides.
• Containers and pots: Fill to within a few centimeters of the rim to allow for watering without overflow. The pot depth itself sets the upper limit.
• New garden beds: Depth requirements vary by soil type, drainage, and intended planting — local nursery or extension service guidance is more reliable than any single universal figure.

Once you decide on a depth, enter it into the calculator. Because depth is so influential, the calculator accepts fractional values — you can enter 4.5 inches, for example, not just whole numbers.

Freshly placed soil — particularly mixes with compost or organic matter — tends to compact over time as it settles under its own weight and after watering. Ordering slightly more than the bare calculated volume helps ensure the bed remains at the intended depth through the first growing season.

The calculator's Extra Material / Settling Allowance option lets you add 0%, +5%, +10%, or +15%, or enter a custom percentage. The results panel then shows the base calculated requirement and the adjusted total side by side.

Example: A base requirement of 32 cu ft with +10% becomes 35.2 cu ft, which requires 47 bags of 0.75 cu ft (rounded up from 46.9). Without the allowance you would buy 43 bags.

The calculator includes an optional, collapsible Soil Mix Composition panel that lets you split your total volume into three component types: Topsoil, Compost, and Potting Mix. The default values (60% / 30% / 10%) are an editable example only — not a universal recommendation for any soil type or planting situation — and can be changed to any percentages that sum to 100%.

The mix breakdown changes only the component volume display in the results panel. It does not alter the total required volume, the bag count, or the cost estimate. Use it as a planning aid to understand roughly how much of each ingredient to source when blending your own garden soil.

For example, at a total volume of 32 cu ft with the default 60/30/10 split, the results show approximately 19.2 cu ft of topsoil, 9.6 cu ft of compost, and 3.2 cu ft of potting mix. Adjust the percentages to reflect the blend you plan to use.

The optional weight estimator (enabled via the toggle in Project Options) calculates an approximate total weight from the soil volume and a density figure. Density presets are available for common soil types — topsoil, raised bed mix, and potting mix — each labeled "Approx" because real soil weight varies significantly with moisture content, organic matter percentage, and compaction level. There is no reliable single universal weight figure for soil.

A "Custom Density" option lets you enter a measured or supplier-stated value if you have one. Results are displayed in both pounds and kilograms. Weight estimates are most useful for logistics purposes — assessing whether a vehicle can carry the load, or how many trips are needed — rather than for precision agronomic calculations.