How much ballast and cement do I need for 1.6m cubed of footings?

For 1m3 of footing you need 2 tonne of aggregate and 10 - 12 bags cement, so for 1.6m3 you need 3.2 tonnes and about 18 bags of cement. Personally I would consider getting a concrete company to deliver 1.6m3. By the time you have all the materials and paid for the labour, it will be cheaper!

or rather than ready mix, get a 'batch on site' truck so you only pay for what you use. ready mix have minimum orders or part load charges

Definitely get a wagon in, ready mixed. Pay for it, then barrow it all in within half hour, job done, put the kettle on.

Hi. You might get away with 2 ballast and 10 cement but to be safe I would get 3 bags of ballast and 15 cement. Rick