I cannot believe the answer to this isn't somewhere in the archives, but
I'll be damned if I can find it!

I'm about to lay a floor screed (approx 3m x 1.8m area) using a 3:1 mix
of sharp sand:cement, using a mixer. I can easily come up with the
volume of wet mixture I need; but where can I find out the number of
bags of cement and sharp sand I need to pick up from Wickes?!!

Cheers
David