Free Growli tool
How much soil for your raised bed
— to the bag.
To find how much soil a raised bed needs, multiply length × width × fill depth. A 4 ft × 8 ft bed filled 12 inches deep takes 32 cubic feet — about 1.2 cubic yards, 906 litres, or 22 standard bags. Enter your own dimensions below to get cubic feet, cubic yards, litres, the exact number of bags to buy, and the ideal 60/30/10 fill mix. No signup.
Enter inside dimensions. Depth is how deep you want to fill — most raised beds use 8–12 inches (20–30 cm) of soil.
You need about
32 ft³
= 1.19 cubic yards = 906 litres = 0.91 m³ of soil.
Cubic feet
32
ft³
Cubic yards
1.19
yd³ (bulk)
Litres
906
UK bagged
Cubic metres
0.91
m³ (bulk)
How many bags to buy
- 22 standard bags (1.5 ft³ each) — the most common US size
- 16 large bags (2 ft³ each)
- 19 UK bags (50 litres each)
You need 1.19 cubic yards — at this volume, ordering bulk soil by the cubic yard is usually far cheaper than bags and saves a lot of lifting. Bagged is fine below about 1 cubic yard.
Recommended raised-bed fill mix
A reliable, well-draining raised-bed mix is roughly 60% topsoil or garden soil, 30% compost for nutrients, and 10% aeration (perlite, coarse sand, or bark fines). For your 32 ft³:
Topsoil (60%)
19.2 ft³
544 litres
Compost (30%)
9.6 ft³
272 litres
Aeration (10%)
3.2 ft³
91 litres
Soil settles 1–2 inches in the first season — top up with compost each spring. See the plant spacing calculator to plan what fits once the bed is filled.
Plan the whole bed in Growli
Once your bed is filled, the Growli app helps you choose what to grow for your light and climate, spaces it correctly, and reminds you when to water, feed, and top up the soil through the season.
Open Growli →How to calculate raised bed soil volume
Soil volume is just length × width × depth. The only trick is keeping the units consistent: if your bed is 8 feet long, 4 feet wide, and you want a 12-inch (1-foot) fill depth, that is 8 × 4 × 1 = 32 cubic feet. Garden suppliers quote soil in cubic feet and cubic yards in the US, and in litres or cubic metres in the UK, so the calculator shows all four at once.
Why depth matters most. Doubling the depth doubles the soil you buy, so it pays to match depth to your crops. Salad leaves and most herbs root happily in 6 inches; the majority of vegetables want 8 to 12 inches; and deep feeders like tomatoes, parsnips, and carrots reward a full 12 inches or more. If the bed sits on a hard surface, add a little extra — roots cannot reach into the ground below.
Buy a little extra. Fresh soil and compost settle 1 to 2 inches in the first few weeks, so order around 5–10% more than the exact figure and top up with compost each spring.
Frequently asked questions
How much soil do I need for a raised bed?
Multiply the bed length by its width by the fill depth to get the volume, then convert to the units your supplier uses. For example a 4 ft by 8 ft bed filled 12 inches deep is 4 × 8 × 1 = 32 cubic feet, which is about 1.2 cubic yards or 906 litres. The calculator does the conversion and tells you how many bags to buy for any size.
How many bags of soil fill a 4x8 raised bed?
A 4 ft by 8 ft bed filled 12 inches deep needs 32 cubic feet of soil. That is about 22 standard 1.5-cubic-foot bags, 16 large 2-cubic-foot bags, or roughly 18 UK 50-litre bags. Filling only 6 inches deep halves those figures.
How deep should a raised bed be?
Most vegetables and herbs are happy in 8 to 12 inches (20 to 30 cm) of soil. Leafy greens and herbs cope with 6 inches; deep-rooted crops like carrots, parsnips, and tomatoes prefer the full 12 inches or more. If the bed sits on solid concrete rather than open ground, add a couple of extra inches because roots cannot grow down into the subsoil.
What is the best soil mix for a raised bed?
A dependable, free-draining raised-bed mix is roughly 60% topsoil or quality garden soil, 30% compost for nutrients and structure, and 10% aeration such as perlite, coarse sand, or bark fines. Avoid filling a bed with pure compost — it holds too much water, slumps badly, and runs out of nutrients within a season.
Is it cheaper to buy soil in bags or in bulk?
Bagged soil is convenient for small beds but costs much more per cubic foot. Once you need about a cubic yard (27 cubic feet) or more, ordering bulk soil by the cubic yard is usually far cheaper and saves carrying dozens of bags. The calculator flags when you have crossed into bulk-ordering territory.
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27, because one cubic yard is 3 ft × 3 ft × 3 ft = 27 cubic feet. To convert cubic feet to litres, multiply by 28.32. The calculator shows cubic feet, cubic yards, litres, and cubic metres at once so you can match whatever unit your supplier quotes.
Does soil settle in a raised bed?
Yes. Fresh soil and compost settle 1 to 2 inches in the first season as organic matter breaks down and the mix compacts. Fill the bed slightly proud of the rim, then top it up with a couple of inches of compost each spring to keep the level and replace nutrients.