Enter each raised bed length, width and fill depth to get the soil volume in litres, cubic feet or cubic yards - plus how many bags to buy. Add a bed for each one you are filling. Works in feet/inches or metres/centimetres.
Typical depths: 50–75 mm (2–3 in) for mulch, 40–50 mm for decorative gravel, 100 mm (4 in)+ for new topsoil, deeper again to fill a raised bed. Each area can take its own depth.
Total bed area
104.0 sq ft
In cubic feet
17.3 cu ft
A raised bed is filled to a depth, so the soil you need is the bed area times the fill depth:
volume = length × width × fill depth
Filling several beds? Add a bed for each one - the calculator totals the volume and rounds the bag count once for the whole order, and it shows a per-bed breakdown so you can see where the soil is going. All math runs in exact metric internally, so switching units never changes the answer.
One 4 ft × 8 ft raised bed filled 12 inches deep, using 1-cubic-foot bags:
In metric, a 1.2 m × 2.4 m bed filled 300 mm deep is 2.88 m² × 0.30 = 0.86 m³ ≈ 860 litres.
Split the total volume from the calculator by your chosen mix:
| Mix | Ratio | Good for |
|---|---|---|
| Standard veg mix | 60% topsoil · 30% compost · 10% aeration | General beds |
| Mel’s Mix | ⅓ compost · ⅓ coir/peat · ⅓ vermiculite | Square-foot gardening |
| Budget deep bed | bulky fill at the base, soil mix on top | Tall beds (hugelkultur) |
Multiply the bed area by the fill depth. A 4 ft × 8 ft bed filled 12 inches deep needs 32 cubic feet (about 1.2 cubic yards, or roughly 900 litres). At 6 inches deep it is half that, 16 cubic feet. Enter your exact bed size and depth above - and add a bed for each one you are filling.
A common, reliable mix is about 60% topsoil, 30% compost and 10% potting or aeration material (such as perlite or composted bark). The popular "Mel's Mix" uses equal thirds of compost, peat or coir, and vermiculite. Work out your total volume here, then split it by your chosen ratio to know how much of each to buy.
Most vegetables and flowers are happy in 250–300 mm (10–12 in) of soil. Root crops like carrots and parsnips prefer 300 mm+ (12 in+). If the bed sits on open ground, roots can grow down further, so you can fill the upper portion with good soil. Set your fill depth in the calculator to match.
For tall beds, fill the bottom third with bulky low-cost material - logs, branches, leaves or coarse compost (a method called hugelkultur) - then top with your good soil mix. To use this, set the calculator depth to only the soil layer you are actually buying, not the full height of the bed.
It depends on bag size: a 4 ft × 8 ft bed at 12 inches deep (about 900 litres) is roughly eighteen 50-litre bags, or about 32 of the common 1-cubic-foot bags. For more than about ten bags, buying topsoil and compost in bulk and mixing your own is usually much cheaper. The calculator gives the bag count for the size you pick.
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