What the raised bed soil calculator does
Raised beds hold more soil than most people expect: a single 8 × 4 ft bed filled 12 inches deep takes 32 cubic feet, and two beds need more than two cubic yards. This calculator adds up every bed so you can decide between bagged soil and a bulk delivery before you start.
Beds of the same size are entered once with a count, and you can add as many different sizes as you need, including metric beds measured in metres and millimetres.
How to use it
- Enter the inside length and width of the bed.
- Enter the depth of soil, which may be a little less than the height of the bed walls.
- Enter how many beds share that size. Add another bed size if your beds differ.
- Optionally add a settling allowance and the bag size you plan to buy.
- Enter a price per bag and a bulk price to compare costs.
Raised bed soil formula
Soil per bed = Length × Width × Depth
Total = Σ (Soil per bed × Number of beds) × (1 + Settling % ÷ 100)
Bags = Total ÷ Bag size, rounded up
In feet, this gives cubic feet; divide by 27 for cubic yards. In metres, it gives cubic metres; multiply by 1,000 for litres. Bagged soil and compost are usually labelled in cubic feet in the US and in litres elsewhere.
Worked example
Two 8 ft × 4 ft beds, filled 12 inches deep:
- One bed: 8 × 4 × 1 = 32 ft³
- Two beds: 64 ft³ = 2.37 yd³ (1.81 m³)
- In 1.5 ft³ bags: 64 ÷ 1.5 = 42.7 → 43 bags
Metric: two 2.4 m × 1.2 m beds filled 300 mm deep hold 2 × 0.864 = 1.728 m³, or 1,728 litres. That’s 35 bags of 50 litres (34.6 rounded up).
Understanding the results
- Soil – the total for all beds, in cubic feet (US) or litres (metric), plus cubic yards and cubic metres.
- Bags – the total divided by your bag size, rounded up.
- Breakdown – volume for each bed size.
- Costs – bagged and bulk costs side by side when you enter both prices.
Filling tips
- Measure inside the bed walls, since thick timber or block walls reduce the soil area.
- Deep beds can be partly filled with coarse organic material at the bottom to reduce the soil you need to buy.
- Leave an inch or two below the rim for mulch and watering.
- New soil usually settles over the first season; topping up later is normal.
What affects how much soil you need
- Settling – fluffy mixes with lots of compost compact after watering.
- Bag fill – bags may be filled loose and compress in storage.
- Uneven ground – beds on sloping ground may be deeper at one end; use the average depth.
Mulching the beds afterwards? Use the mulch calculator. For other volumes, try the cubic feet calculator or the cubic yard calculator.