Raised Bed Soil Volume Calculator
Filling a raised garden bed with the right amount of soil is a simple volume calculation: multiply the bed's inside length by its inside width by the depth you want to fill, keeping all three measurements in the same units. This calculator returns that volume in cubic feet, the unit bagged soil is usually sold in, and also converts it to cubic yards for bulk deliveries. The one thing to get right is to measure the inside of the frame, not the outer dimensions, since the timber or block walls take up space the soil does not fill. For an 8 foot by 4 foot bed filled to a depth of 6 inches, which is 0.5 feet, the volume works out to 16 cubic feet. It is wise to treat the result as a minimum, because fresh soil and compost are fluffy and settle over the first season as they are watered, so buying a little extra or topping up later keeps the bed at a good level. Leave a small gap below the rim so soil does not spill when watered. Every figure here is computed deterministically from the length times width times depth formula below, with a worked example that reconciles exactly to the calculator.
Soil volume is length times width times fill depth: volume = L x W x depth. An 8 ft by 4 ft bed filled 0.5 ft (6 in) deep needs 16 cubic feet of soil, about 0.59 cubic yards.
Soil volume formula
volume (cubic feet) = length x width x depth
length, width = inside dimensions of the bed
depth = fill depth, all in feet
cubic yards = cubic feet / 27
Multiplying the inside length, width and depth gives the soil volume. Dividing by 27 converts cubic feet to cubic yards for bulk soil orders.
Worked example
An 8 foot by 4 foot raised bed is filled to a depth of 6 inches (0.5 feet).
- Base area: 8 x 4 = 32 square feet.
- Volume: 32 x 0.5 = 16 cubic feet.
- In cubic yards: 16 / 27 = 0.59 cubic yards.
You need 16 cubic feet of soil. These are the calculator's default inputs, so the result above matches the widget exactly.
Raised bed soil calculator: frequently asked questions
How much soil does a raised bed need?
Multiply the bed's inside length by its inside width by the fill depth, using the same units, to get the volume. For an 8 foot by 4 foot bed filled 6 inches (0.5 feet) deep, that is 8 times 4 times 0.5, which is 16 cubic feet of soil. Always measure the inside dimensions, not the outer frame.
How do I convert cubic feet to cubic yards?
Divide the cubic feet by 27, because one cubic yard contains 27 cubic feet. Bulk soil and compost are often sold by the cubic yard, so 16 cubic feet is 16 divided by 27, about 0.59 cubic yards. Bagged soil is usually sold in cubic feet, which makes the cubic-foot figure convenient.
Should I fill the bed to the very top?
Leave a small gap, often an inch or two, below the rim so that soil and mulch do not spill over when watered. Soil also settles after the first few waterings, so it is common to slightly overfill at planting and top up later. Account for this by treating the calculated volume as a minimum.
What should I fill a raised bed with?
A typical mix blends topsoil or garden soil with compost and sometimes other organic matter for drainage and nutrients. The right blend depends on what you are growing and your local conditions. State and university extension services, and federal resources, publish guidance on soils suited to home growing.
Does soil settle over time?
Yes. Fresh soil and compost are fluffy and compact down over the first season as they are watered and as organic matter breaks down, so the bed will need topping up. Buying a little extra soil, or planning to add compost each season, keeps the bed at a good level for healthy root growth.
Official sources
- Soils, land and water resource information: US Geological Survey (USGS). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.