How to Fill a Raised Bed (and How Much Soil You Need)
Last updated: September 2026
Raised beds are brilliant for growing vegetables and flowers, especially if your soil is heavy clay or you want to avoid bending. They take a surprising amount of soil to fill, though. Here's what to put in them and how to work out how much to buy.
How much soil does a raised bed hold?
Multiply length × width × height in metres to get cubic metres, then multiply by 1,000 to get litres.
A typical 2.4m × 1.2m bed that is 30cm deep holds 2.4 × 1.2 × 0.3 = 0.86m³, or 864 litres. That's around 15 bags of 60 litres, which is why a bulk bag is often better value for bigger beds.
Add about 10–20% extra because soil and compost settle after watering. If you're building several beds, the Raised Bed Calculator works out the total and the cheapest way to buy it.
The best mix for a raised bed
A good all-round filling is roughly 60% topsoil and 40% compost. Topsoil gives the bed structure and holds water; compost adds nutrients and organic matter. Pure compost shrinks down fast, dries out quickly and can be too rich for some plants. Pure topsoil can be heavy and low in nutrients.
For the 864-litre bed above, that's about 520 litres of topsoil and 345 litres of compost.
Saving soil in deep beds
For beds deeper than about 45cm, you don't need good soil all the way down – most plant roots work in the top 30–40cm. You can fill the bottom third with:
- untreated logs and branches (they break down slowly and hold moisture)
- turf removed from the site, placed grass-side down
- garden prunings and leaves
This is sometimes called the “lasagne” or hügelkultur method. Expect the bed to sink a little as the lower layers rot, and top it up with compost each year.
Don't put builders' rubble, plastic or treated timber offcuts in the bottom of a bed you'll grow food in.
What size should a raised bed be?
Width: 1.2m maximum if you can reach from both sides, 60–75cm if against a wall or fence. You should reach the middle without stepping on the soil.
Height: 20–30cm is fine for most vegetables on decent ground. 45cm or more is kinder on backs and good over poor soil or paving.
Length: whatever fits, but leave paths at least 45cm wide – wider if you need a wheelbarrow through.
Choosing materials
Pressure-treated timber, new railway-style sleepers, galvanised steel and brick all work well. Avoid old railway sleepers soaked in creosote for food growing – creosote is no longer sold for home use and can leach into the soil. Lining the inside of timber beds with a permeable membrane helps them last longer.
Filling it step by step
Level the ground and remove perennial weeds.
Lay cardboard on the base if you're building over grass – it smothers the grass and rots away.
Add any bulky base layer (for deep beds).
Fill with your topsoil and compost mix in layers, lightly firming each one.
Water well and let it settle for a few days before topping up and planting.
Frequently asked questions
Can I fill a raised bed with just compost?
You can, but it will sink noticeably, dry out quickly and may be too rich. Mixing in topsoil gives better structure.
How deep should a raised bed be for vegetables?
At least 30cm for most crops. Root vegetables such as parsnips prefer 45cm or more.
Is a bulk bag cheaper than bags of compost?
Usually, once you need more than about 300–400 litres. Check the delivery charge and make sure you have somewhere to put it.
How often should I top up a raised bed?
Add 5–10cm of compost each year, usually in autumn or early spring.