If you are buying a jug, get 1.5L or more. I don't know the exact qty the bike holds. I bought a jug 1.89 L, there is lots left after fully filling.
If you are just wondering how much to put, do the following:
1. Fill rad until top fins are submerged. Bleed cooling system as per manual (loosen bleeder bolt near spark plug, wait till bubbles stop coming out, tighten bolt).
2. By now the level in the rad will have decreased slightly. Fill rad till fins are submerged.
3. Let bike idle for 30 s. Don't let bike get hot, just let the coolant circulate.
OR
Take the bike for quick, cautious ride. Let it fully cool.
4. Fill rad until fins are submerged by 10 mm.
You should keep the fins under 10 mm of coolant (when bike is cold). I check every ride or two.
I found that the rad will lie when initially filling... it looks full, but rock the bike side to side and the coolant level will drop (I guess the rad gets air bubbles trapped in it or something). This is why it's a good idea to check coolant level periodically.