Do them from cold. However I've tried a few different home air pumps and you'd be surprised how far off the gauges read when comparing to a calibrated gauge. I bought a brand new foot pump, inflated tyres to the manufactures spec of 36psi, checked with a calibrated gauge and I only had 31psi. checked with another shop bought gauge I had lying about and I got 38psi. If you want your tyre pressures to be spot on then get your hands on a calibrated gauge and get it checked a couple of times a year, ours at work were done every 3 months.