Oxy-acetylene

We need to order more oxygen and acetylene. How do you figure out what to order? Mostly it is by CF or cubic feet of gas in refilled bottles. Just ordered a 150 CF bottle of oxygen for  $15.71 and a 100CF bottle of acetylene for $96.70.

http://www.tricowelding.com/cylinder_sizing/hp_sizing_chart_1-10-11.pdf