I have found the gauge to be an indicator ONLY, the reserve light is a lot more accurate and i have found this to be consistently accurate.
When that light comes on, you have got approx 6 litres of fuel remaining (1 1/3 gallons uk). That gives me at least 30 miles or more in 'touring mode' to find a fill up.
So you still had a good few miles to go before you would have run dry