Well, it depends on a lot of things man... Changing it over to numbers I can do the math on, and assuming your light comes on about the same place as mine (with ~14.5 gallons used), you're looking at about 13.5 miles per gallon, or to you, err... well, I'm not entirely sure how you guys measure fuel consumption. To say the least though, that's not so good. I'm pretty sure my 1j gets at least 15+ mpg, and I boost the thing pretty much every day...
Have you been keeping up on your maintenance?