A sleeper bed is built in courses, one sleeper high each. The count depends on how many courses you need and how well the sides fit the length of the sleepers you can buy.
Courses
Sleepers are laid on their edge. A 200 mm face gives 200 mm of height a course, so a 400 mm bed is two courses and a 600 mm bed is three.
Wickes lists a 2.4 m sleeper at 200 × 100 mm. Bunnings lists treated pine at 200 × 75 mm, in 1.8 m, 2.4 m and 3.0 m lengths.
Sides that fit the sleeper
A 2.4 m by 1.2 m bed is the easy one. Each long side is one whole sleeper, and one sleeper cut in half makes both short sides. That is three sleepers a course, six for 400 mm.
A 1.8 m by 0.9 m bed also takes three a course: each 1.8 m side leaves a 0.6 m offcut, which is not long enough for a 0.9 m end, so the ends need their own sleeper.
| Bed | 200 mm high | 400 mm high | 600 mm high |
|---|---|---|---|
| 1.2 × 1.2 m | 2 | 4 | 6 |
| 1.8 × 0.9 m | 3 | 6 | 9 |
| 2.4 × 1.2 m | 3 | 6 | 9 |
| 3.0 × 1.5 m | 4 | 8 | 12 |
| 2.4 × 2.4 m | 4 | 8 | 12 |
| 3.6 × 1.2 m | 4 | 8 | 12 |
Reusing offcuts
The calculator cuts the longest pieces first and fits each new piece into an existing offcut when it is long enough. Only then does it open a new sleeper. It does not join two short pieces inside one side.
A 3 m by 1.5 m bed shows how: each 3 m side is a whole sleeper plus a 0.6 m piece, and each 1.5 m end comes out of the same sleeper as one of those pieces. That is two whole and two cut sleepers, four a course.
Filling it
Sleepers are 75 to 100 mm thick, so the inside of the bed is smaller than the outside. Use the inside size in the Raised bed calculator to count bags of soil.
Figures are estimates for a shopping list. Check the pack or datasheet before you buy.