Toyota usually has a buffer of 10 litres when the light comes on so take your current consumption and assume 10 litres remaining and that'll give you a rough estimate of the remaining distance left after the low fuel light comes on.
at 10 liters of fuel remaining you'll get 178 km ( 110 miles), as @Tideland Prius pointed out, if you use the EPA 42 mpg combined. If you're not a particularly efficient driver, just want to get from point A to B, I'd assume 35 mpg which will get you about 165 km (103 miles). BTW 10 litres is about 2.6 gallons of gas which sounds about right from my fillups.
