Raised Bed Soil Calculator
Filling a raised bed takes more soil than most gardeners expect. A single 8 × 4 ft bed that is 12 inches deep holds 32 cubic feet – that is more than twenty 1.5 cu ft bags. This calculator multiplies length × width × depth for each bed, adds them together and converts the total into cubic feet, cubic yards, liters and the number of bags in the most common retail sizes.
How to use this calculator
- Choose imperial (feet and inches) or metric (meters and centimeters).
- Enter the inside length, width and soil depth of your bed. Measure the inside, not the outside of the boards.
- If you have several beds of the same size, set the quantity. Use “Add another bed” for different sizes.
- Tick the settling option if you are filling with fresh, fluffy mix – it compacts over the first few weeks.
- Read the total volume and the number of bags for each bag size. Bulk soil is usually sold by the cubic yard (US) or cubic meter.
How the calculation works
Volume = length × width × depth. With imperial units the depth is entered in inches and divided by 12 to get feet, so an 8 ft × 4 ft × 10 in bed is 8 × 4 × 0.833 = 26.7 cubic feet. One cubic yard is 27 cubic feet and one cubic foot is about 28.3 liters. Bag counts are always rounded up, because you cannot buy part of a bag.
Bags or bulk?
Bagged mix is convenient for one or two small beds. Once you need more than about one cubic yard (roughly eighteen 1.5 cu ft bags), bulk delivery from a landscape supplier is often cheaper, even after a delivery fee. Ask whether bulk material is sold by loose volume, and remember a cubic yard of damp soil can weigh well over a thousand pounds.
What to fill a raised bed with
A widely used starting point is a blend of good topsoil and compost, often around 60% topsoil to 40% compost, sometimes with a little coarse material such as pine bark fines for drainage. Pure compost or pure bagged potting mix tends to shrink and can be costly at this scale. For very deep beds, some gardeners fill the bottom with logs, branches or leaves to reduce how much purchased soil they need – the top 12 inches or so should still be quality soil.
Frequently asked questions
How much soil do I need for a 4×8 raised bed?
A 4 × 8 ft bed holds 2.67 cubic feet for every inch of depth. At 6 in deep that is 16 cu ft, at 10 in about 26.7 cu ft, and at 12 in 32 cu ft (about 1.19 cubic yards).
How many bags of soil fill a raised bed?
Divide the bed volume in cubic feet by the bag size. A 32 cu ft bed needs 22 bags of 1.5 cu ft, 16 bags of 2 cu ft, or 32 bags of 1 cu ft. The calculator rounds up for you.
Should I add extra soil for settling?
Yes, if you are filling with loose new mix. Soil typically settles over the first season, so adding around 10% or topping up after a few weeks keeps the bed full.
How deep should a raised bed be?
Most vegetables grow well in 8 to 12 inches of loose soil. Root crops such as carrots and parsnips benefit from 12 inches or more, while lettuce and herbs cope with about 6 to 8 inches.
Does the calculator work for round or L-shaped beds?
Split an L-shaped bed into two rectangles and add each as its own bed. For a round bed, use the mulch calculator’s circle option to get the area, then multiply by depth.