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Choose your bed shape, enter dimensions and depth — we'll tell you the volume and how many bags to buy.
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How Much Compost Do I Need?
This free compost calculator works out exactly how much compost you need for raised beds, garden borders, vegetable plots and containers. Enter your dimensions and depth, and get instant results in litres, cubic metres and bag counts for all the standard sizes you'll find in garden centres.
Buying the wrong amount wastes money — too little means another trip, too much means bags of compost sitting in the rain going to waste. Get it right first time.
Compost Bag Sizes & Coverage
UK garden centres sell compost in several standard bag sizes. Here's how much area each covers at different depths.
| Bag Size | Coverage at 5cm | Coverage at 10cm | Coverage at 20cm |
|---|---|---|---|
| 40 litres | 0.8 m² | 0.4 m² | 0.2 m² |
| 50 litres | 1.0 m² | 0.5 m² | 0.25 m² |
| 60 litres | 1.2 m² | 0.6 m² | 0.3 m² |
| 100 litres | 2.0 m² | 1.0 m² | 0.5 m² |
| Bulk bag (1m³) | 20.0 m² | 10.0 m² | 5.0 m² |
Tips for Buying Compost
Raised beds
For new raised beds, a 60/40 mix of multi-purpose compost and topsoil is ideal. It gives good drainage while retaining enough moisture and nutrients. Pure compost shrinks as it breaks down, so expect to top up after the first season.
Topping up borders
A 5cm layer of compost spread over existing borders in spring acts as a mulch and slow-release feed. Fork it lightly into the top few centimetres rather than burying it deep — worms will do the rest.
Saving money on large areas
If you need more than 500 litres, a bulk bag (1m³ = 1,000 litres) is usually 50–60% cheaper per litre than individual bags. Many garden centres and builders' merchants deliver bulk bags for free over a certain order value.