Raised Bed Soil Volume Calculator
Knowing exactly how much soil you need before visiting the garden center saves money and trips. This calculator multiplies your raised bed's length, width, and depth to give the total cubic feet of soil required, then converts that into the number of standard 1 or 2 cubic foot bags. Enter your bed dimensions (the tool accepts either feet or inches for depth), and optionally adjust the bag size to match what is sold locally. The USDA National Gardening Association recommends filling raised beds with a blended mix rather than native soil to ensure drainage, aeration, and fertility.
Raised bed soil volume formula
Volume (cu ft) = Length (ft) x Width (ft) x Depth (ft)
Bags = ceil(Volume / Bag size)
Convert depth from inches to feet by dividing by 12. For example, a 12-inch deep bed has a depth of 1.00 ft. Round the bag count up to avoid running short.
Choosing the right soil depth
- Leafy greens (lettuce, spinach): 6 inches minimum, 8 to 12 inches ideal.
- Most vegetables (tomatoes, peppers, beans): 12 inches minimum.
- Root crops (carrots, parsnips): 18 to 24 inches for best results.
- Add 10 to 20 percent extra volume to account for natural settling after the first season.
- A standard 4 x 8 bed at 12 inches deep requires 32 cubic feet, or 16 two-cubic-foot bags.
Raised bed soil calculator: frequently asked questions
How do I calculate raised bed soil volume?
Multiply length by width by depth (all in feet). For example, a 4 ft x 8 ft x 1 ft bed needs 32 cubic feet of soil. Convert inches to feet first by dividing by 12.
How many bags of soil do I need for a raised bed?
Divide the total cubic feet by the bag size. A 2 cubic foot bag is common. A 4 ft x 8 ft x 1 ft bed needs 32 cu ft, so 16 two-cubic-foot bags. Always round up to the nearest whole bag.
How deep should a raised bed be?
Most vegetables need 12 inches (1 foot) of soil depth. Root vegetables like carrots need 18 to 24 inches. Shallow-rooted greens can grow in as little as 6 inches. USDA extension guides recommend a minimum of 12 inches for general vegetable production.
What is the best soil mix for a raised bed?
A common USDA-recommended mix is one third compost, one third peat or coir, and one third coarse vermiculite or perlite. This provides drainage and nutrients. Avoid filling beds with pure garden soil, which compacts over time.
Do I need to account for soil settling?
Yes. Raised bed soil typically settles 10 to 20 percent after watering. Add 10 to 20 percent extra to your calculated volume, or plan to top up the bed after the first season.
Official sources
- USDA National Institute of Food and Agriculture: nifa.usda.gov.
- USDA Agricultural Research Service: ars.usda.gov.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.