Bolt and screw lengths are always stated according to the effective length. Therefore, a normal hex-headed bolt or cap screw or round or pan headed screw are all measured from under the head, to the end of the thread. A screw or a bolt with a normal countersunk head is measured overall. Raised or domed countersunk screws are measured from the widest end of the cone, where the dome meets the cone, to the end of the thread.