Until it can no longer support life? Between 1 and 1.5 billion years. Until it is enveloped by the sun, or destroyed by it? About 4 to 5 billion years.
Generally there is a 12-1 ratio. Just like the ratio of Fahrenheit to Celsius. As Celsius is how we measure the temperature on the moon, so is the years we measure.
An Earth year is a measure of the time it takes for the earth to make one complete orbit of the sun. So this is actually a unit of time. A light year is the distance light will travel in one Earth...
The following is the number of days (approximately) that it takes for each planet to orbit the Sun:Mercury 87.6Venus 222.65Mars 686.2Jupiter 4,332.55Saturn 10,749.25Uranus 30,685.55Neptune 60,188.5