Well you could use ready mix, only one thing...they like to dump it in a pile and if you have not calculated in properly which even with my experience I end up having a couple of barrows over or under.
Then you could use a barrow mix service, they mix it at the door for you. A little more expensive but you get exactly what you want, only problem is that they like to barrow it to you like concrete was going out of fashion, not nice if you are trying to lay a floor.
Then there is the 'old fashioned' way of hand batching it:
As a rule of thumb, one cubic metre of wet concrete weighs 2.5 metric tonne, calculate that into your cubic requirement and we get 3.25 tonne. If we use a ratio of 4:2:1 and calculate there is 1000 kg in a tonne bag, you could use a 'bag' method and say there is 20 bags (8st or 50kg) per tonne...sooo... 4 bags of gravel...2 bags of sharp sand...and one bag of cement (two actually because you only get then in half bags now:25kg)
Put that into our equation and we get approx 10 mixes
Now you can only get one tonne bags delivered so I would order two 1 tonne bags of pea gravel, one 1 tonne bag of sharp sand and twenty 25 kg bags of cement..oh and a bit of water..
I hope this helps but I warn you it will be hard work and you will never have calculated exactly your cubic requirements so you you might need a little bit more or you might have some left.
