Planning a new bed
Mark the outline with a hose or string before you dig, then measure it. Beds wider than about 4 ft (1.2 m) are hard to reach into from both sides, so add a stepping path if you go bigger.
Planning the rest of the job? Use the Raised bed soil calculator and the Garden soil calculator too.
How much soil and mulch?
Improve existing soil, dig in
2 to 3 in (5 to 7.5 cm) of compost
New bed on poor ground
6 in (15 cm) of garden soil
Mulch on top
2 to 3 in (5 to 7.5 cm)
Edging
Length of the outside edge
How does the calculation work?
Volume = area × depth
A bed 10 ft by 4 ft with 6 in of soil: 40 ft² × 0.5 ft = 20 ft³, or 0.74 yd³. Mulch at 3 in adds another 10 ft³. Edging runs 28 ft.
For a round bed, the area is 3.14 × radius × radius, and the edge is 3.14 × the diameter.