How the raised bed calculator works
Each layer (course) of a sleeper bed has two long sides and two short sides. The short sides fit between the long ones, so they're the bed width minus two sleeper thicknesses. The calculator lists every piece and packs them into the fewest full sleepers, reusing offcuts.
Popular bed sizes (2400 × 200 × 100mm sleepers)
| Bed size | Height | Sleepers | Soil to fill |
|---|---|---|---|
| 2.4 × 1.2m | 200mm (1 high) | 3 | ~0.51 m³ |
| 2.4 × 1.2m | 400mm (2 high) | 6 | ~1.01 m³ |
| 1.2 × 1.2m | 400mm (2 high) | 4 | ~0.46 m³ |
| 2.4 × 1.2m | 600mm (3 high) | 9 | ~1.52 m³ |
Soil figures include 15% extra for settling.
Building tips
- Level the ground first, or bed the bottom course on a little sharp sand so it sits flat.
- Overlap the corners on alternate courses, like brickwork, for a stronger bed.
- Fix with two 200mm timber screws at each corner per course. Tall beds benefit from a 75 × 75mm post inside each corner.
- For vegetables, choose sleepers treated with modern preservatives, or line the inside walls. Avoid old creosoted railway sleepers.
Worked example: a 2.4m × 1.2m veg bed, two sleepers high
Each course needs two 2.4m long sides and two short sides of 1.2m − 2 × 0.1m = 1.0m. Over two courses that's four full sleepers plus four 1.0m pieces. Two 1.0m pieces come out of each sleeper, so 6 sleepers in total, with four cuts and two 0.4m offcuts left for a step or edging. The bed stands 400mm high and holds about 2.2m × 1.0m × 0.4m = 0.88m³, or about 1m³ of soil with settling. That's two 0.75m³ bulk bags of a 60:40 topsoil and compost mix. You'll need 16 long timber screws and about 3m² of liner for the inside walls.
Getting the size right
- Width: 1.2m lets most people reach the middle from either side without stepping on the soil. Against a wall or fence, keep it to about 0.9m.
- Length: 2.4m uses whole sleepers with no cuts on the long sides. Longer beds need a joint, which should be staggered between courses.
- Height: 400–600mm means much less bending. Taller beds suit people who find kneeling hard but take a lot more soil to fill.
- Paths: leave at least 450–600mm between beds for a wheelbarrow.
Filling a tall bed for less
Deep beds don't need good soil all the way down. Many gardeners fill the bottom third with upturned turf, woody prunings or rotted leaves, then top it with at least 300mm of topsoil and compost. The lower layers break down over time, so expect to top up the bed each spring. The topsoil calculator works out bulk bags for any depth.
Common mistakes
- Uneven ground. A bed that isn't level opens gaps at the corners. Level the base, or dig the bottom course in slightly.
- Fixing with short screws. Sleepers are heavy and move as they weather. Use proper 200mm timber screws, two per corner per course.
- Lining the base. A solid base stops drainage and roots. Line only the inside walls.
- Old railway sleepers for food growing. Reclaimed creosote-treated sleepers can leach oils. Use new treated or hardwood sleepers.
Holding back a slope instead? A sleeper retaining wall needs posts set in concrete and drainage behind it. See all garden and landscaping calculators.