Do you need to know exactly or are you just trying to order coolant? I can tell you my loop with GTX360, CPU and GPU blocks and a radikult custom panel radiator (probably holds 100-200mL but again guessing) was under 600mL. The part that holds most of the fluid are the tanks on the end, so the size difference won't make a huge difference. If I had to guess I'd say about 250mL, but that's just a guess. In other words, I don't see your loop using more than 1L of coolant unless its crazy.