How much compost will I need?

[HugoDarracott]

I'm currently digging a new bed. I've taken up some artificial turf and digging out all the sand and hardcore. I've done this before and I ended up having to buy tonnes of compost to fill the hole. I massively underestimated how much I'd need. How do you work out the volume of compost required?

How big is the area and how much below the lawn level did you dig?

Personally, I'd use good quality top soil over compost as compost will degrade. Or you could add a mix of mainly top soil with some compost added in.

Length x width x depth, in metres. Gives the volume in cubic metres. Each cubic metre would be 1000 litres. That works quite well for topsoil too.

So if your new bed is 2m x 1m and 20cm deep, it would be 2 x 1 x 0.5 = 1 cu m = 1000l. So about 14 70l bags.

Do you actually need compost? Could you not get away with topsoil?

If you were filling it with water, 1 cu m /1000l would be 1 tonne. Topsoil isn’t far off the density, so the same conversion would be reasonable. Compost is a bit less dense.

@HugoDarracott There are online calculators for example:
https://www.lovethegarden.com/uk-en/calculator/compost
https://www.compostdirect.com/calculator

For veg 1/3 manure, 1/3 compost, 1/3 top soil is good for raised beds.

I'm not sure if I can get away with topsoil as I'm creating a bed for ericaceous plants. Thanks for the calculation, bed is approx 2 by 1 by 0.5m

I can get some free soil off Facebook market place but obviously no idea of pH.

Never trust a mathematician to do sums! 20cm is 0.2m not 0.5, so it's 2 x 1 x0.2 = 0.4 cu m = 400 l or about 6 x 70l bags. Sorry about that!

This.