Adding grit to soil mix

That is cubic centimetres, so divide by 1000 to get litres. So that's 43 litres.

 

@CarolineL Thanks. That I can work with.

G.

 

I mix according to eye these days.....according to the plant and its free draining needs. Seems to work well for me how the compost feels and looks helps identify how well drained it will be.
Perlite or grit? For extra weight and stability I use grit. Don’t use sand now as I found it less effective than fine grit.