That's based on so many potential factors. It's all dose dependent. For example, right now I'm using Test 250mg/ml @ 750mg/wk. That means that I get 3 weeks and 1/3 of an injection each vial. If I was only running 250mg/wk it would last me 10 weeks, but if I was running 1250mg/wk it would only last me 2 weeks.
This is how I figure out how much I need. I'll use my current cycle as an example:
16 weeks @ 750mg/wk = 12,000mg total
2,500mg are in each vial (250mg/ml 10ml)
12,000/2,500 = 4.8 vials... That would mean 5 vials are needed.
Hope this helps.