there is no real set mixing ratio, it's all based on the temperature, how old the paint is, how many times you opened the can, and which way the wind is blowing!!! you just have to have a "feel" for it. i've painted in both extreems of temperature, from about -10 deg celcus to +30 deg celcus and never had a problem with the paint having any bad habbits, but the mixing ratio was higher the colder it was.