Okay, daft question coming.

Just want to get my tyre pressures correct and it's the manuals fault. They say the pressure should be measured at an ambient 20*C. I know the pressures increase as the temperature rises so...

Now I'm obviously not going to wait until it warms up as it was only 15*C today. So, simple enough question albeit daft and perhaps I'm taking this too seriously, but what would be the pressure loss of pressure for the 5*C difference. If that makes sense. I mean if the pressure in the rear tyre was 40lb/in2 as 15*C then the pressure would be higher at 20*C.