no you should check your oil when it is warm also, just let the engine sit for like a minute before checking it (lets some of the oil go back down into the sump) then wipe the dip stick off stick in then check it.
This is because liquids expand when they are heated up, this the same principel with tires, if you fill your tires with 35 psi when it is 90 out and you have just stop from a long road trip, then in the winter when it is like 11 out, your tire pressure is only going to be like 31 psi