Raised Garden Bed Calculator
Enter the bed's outside dimensions and how tall you want it. We'll size the soil and the lumber to build it.
Advanced options
- Internal volume
- 0 cu ft
- Bed area
- 0 sq ft
- Lumber courses (rows)
- 0
- Boards needed
- 0
- Corner stakes / brackets
- 4
- Deck screws (3" / 75 mm)
- 0
- Soil bags (1 cu ft)
- 0
- Estimated cost
- —
How the raised bed calculator works
Soil: internal volume = (length − 2 × board thickness) × (width − 2 × board thickness) × bed height. Then convert to cubic yards (or m³). Add 5% waste for settling and gaps. The calc assumes 1½" / 3.8 cm board thickness for standard 2× lumber.
Lumber: rows of boards = bed height ÷ board face width, rounded up. Boards per row = (2 × length + 2 × width) ÷ board length, rounded up. Corner brackets or 4×4 stakes at each corner; 3" deck screws every 12" along seams.
Soil mix recipe
Mel's Mix and similar formulas: 1/3 topsoil, 1/3 compost, 1/3 vermiculite or peat moss by volume. So a 32 cu ft bed needs ~10 cu ft of each. Our calculator gives the total volume; split it across the three components when ordering.
Wood choice
- Cedar / redwood — naturally rot-resistant, no chemicals, food-safe. Lasts 10–15 years. $3–6 per linear foot for cedar 2×6.
- Pressure-treated (modern ACQ/MCA) — modern PT lumber uses copper-based preservatives that are food-safe. Lasts 20+ years. $1.50–3 per linear foot. Avoid older CCA-treated wood (pre-2003).
- Plain pine / fir — cheapest but lasts 5–7 years before rotting through. Acceptable for short-term beds; not for long-term gardens.
- Galvanized metal raised beds — buy assembled; not in this calc.
Bed height by use
- 6 in / 15 cm — for shallow-rooted greens (lettuce, herbs, radishes). Cheapest, less soil needed.
- 12 in / 30 cm — the sweet spot for most vegetables. Good root depth, accessible bending height.
- 18–24 in / 45–60 cm — accessible for standing or sitting. Older gardeners and ADA accommodations.
- 24+ in / 60+ cm — wheelchair-accessible, deeper roots for tomatoes/peppers.
Common questions
What goes on the bottom of the bed?
Cardboard or several layers of newspaper, directly on the lawn or soil. It blocks weed growth for the first year while it composts in place. No need for landscape fabric — that prevents proper soil mixing with the underlying soil and earthworms.
How much does a 4×8 raised bed cost?
Lumber (cedar): $80–$160. Soil mix: $80–$160 for 32 cu ft. Brackets + screws: $20. Total DIY: ~$200–$340. Pre-built cedar kits run $200–$400 for the same size; you save 30–50% by building it yourself.
Can I stack 2×6 boards instead of using 2×12?
Yes — two courses of 2×6 = 11" tall, very close to a single 2×12. Pros: easier to handle, can level corners independently. Cons: more screws, more seams to seal, slightly less rigid against soil pressure. For beds under 4 ft long, stacked 2×6 is fine; longer beds benefit from solid 2×12 walls.
For the soil itself, see the topsoil calculator. For mulch around or on top of beds, the mulch calculator.