Here is a related rule of thumb which I developed, when wondering about the effects of temperature changes between Winter and Summer.
Forgive any rounding off in the mathematics. But for moderate places in the US, I presume that the 30 psi (cold) would be meant to take place at around 50 degrees F (=283 Kelvin). Generally the worst that can happen to you is that in Summer it goes up to 100 deg F (=313 K), and in Winter it can go down to zero F (=253 K).
I cheated a little bit, but it makes it easier to remember. It boils down to my rule that
RULE going up or down 50 deg. F makes the pressure RULE go up or down by 3 psi. RULE
Or another way of wording it, using "ballpark" figures that most cars require a pressure of about 30 psi, then going up or down about 10% in temperature (on the absolute Kelvin scale) makes the pressure go up or down also by 10% of 30 psi, which = 3 psi.
I find it useful to have run through this exercise, so that I know to expect that, even if my tires do not leak, almost the worst that will happen is that the pressure will range from 27 to 33 psi over the course of the practical (almost) extremes of a year.