A garden is nothing if it has no soil. In this blog we’re looking at how to calculate topsoil quantities…because it’s important to have enough.
How to tell if you need more topsoil
Sometimes it’s obvious that you need to order in some soil. For example if you are building raised beds or terraces and want to fill them with quality growing material.
Scroll down to find out how to work out the amount of soil you need for your containers.
Do you need soil for turfing?
If you already have soil in your garden and you want to lay turf, how can you tell if you need more topsoil.
Turf, and indeed most plants, need a depth of around 15cm of good quality growing medium to sink their roots into. The exceptions are tree planting where deeper soils are needed. And green roofs where there may be issues with the weight.
How do you know how much soil is already in your garden. A standard garden fork has prongs of around 23cm long. If you can push the fork right into the soil anywhere in your garden, then the soil is deep enough for turf, herbaceous perennials and bedding plants.
The only reason you might need new soil is to improve the quality.
Calculating quantities for topsoil
Here’s a quick guide to calculating how much topsoil you need to buy.
- First of all measure the length and the width of the area you’ll be adding soil to.
- Then make a note of the depth of topsoil you need.
- I find it easiest to work in metres – it means less maths overall.
- Multiply the length by the width to get the area
- Now multiply the area by the depth
- This will give you a figure in cubic metres.
- Divide the figure by 0.9 to work out how many big bags of soil to buy
Let’s say you want to fill 6 raised beds with soil
If each raised bed is 1.3 metres long x 1.3 metres wide by 50cm (0.5 metres) deep The calculation will look like this
To find the volume of 1 raised bed
Multiply the length by the width
1.3m x 1.3 m = 1.69 square metres
Next multiply that figure by the depth
1.69 x 0.5 = 0.84
Total volume of soil needed
There are 6 raised beds so multiply 0.84 by 6
0.84 x 6 = 5.04
You need 5.04 cubic metres of soil.
One bulk bag of soil contains 0.9 cubic metres.
5.04 divided by 0.9 is 5.6
You actually need 5.6 bags of soil.
You could either: round that up to 6 bags and have some left over for other projects in the garden
Or order 5 bags of soil and only fill your raised beds to within a few centimetres of the top.
Help with calculations
Please don’t struggle with complicated calculations – there’s nothing worse than being short of soil and nothing so annoying as paying for soil you don’t need.
All you need to do is make a note of your measurements and contact the Stewarts Turf team who will be pleased to help you calculate your needs.
Where to buy topsoil in Scotland
More topsoil advice