How hot is the room you're in? Common sense tells you that the CPU cannot be colder than the air being used to cool it down. So, if you want a rough estimation of cpu temp, turn on the computer after it's been sitting for several hours and immediately jump into the bios to see what the CPU temp is. Write that down and compare it the the room temp. Whatever the difference is, add that to whatever program displays the the temps from BIOS, plus maybe throw in another degree or two to be safe.
OR, just say good enough and forget about it. Whatever.