How much paint is needed to paint a gas tank?

Hello,
This question might be a bit vague but I'm not looking for a precise answer, just a ballpark figure. I have a 1985 Kawasaki Eliminator 900 which has more of a cruiser-style gas tank (smaller than the one on Vulcan Mean Streak), more tear-shaped and flat than tall. I'd like to paint it a solid color, no patterns. There is a specific paint that I'd like to get that is sold in 100 mL (3.4 oz), 250 mL (8.5 oz), 500 mL (17 oz) and 1L (33.8 oz) cans. This is for base coat only, tank is already primed and glossy top coat doesn't matter. I'd like to buy the paint and bring it to the paint shop so they don't need to match the color. Any idea which of those can sizes would be enough to paint the tank (top side only, bottom will be black) ?
Thank you,
Katz

Base coat colors typically need to be cleared within a specified, fairly short, period of time.  Unless you make arrangements with the shop to clear it right away, after you deliver the tank, it might be better to just let them do the whole job.

To answer the question, the smallest contain should be enough for just a tank, assuming the paint is somewhat thick, and you reduce it by 20% or so, increasing the sprayable material some.

I think you're right, better let the paint shop handle this. Just need to talk to them to see if they can get the color I'm looking for.
Thank you,
K