Just keep in mind the wide variation in "ear length". While I would agree with CSutton about a 24" average, that means ears could be 18 to 26".
I shot a buck in western wyoming and the ears were 26" tip to tip. My friend shot a buck in eastern Idaho this year and the ears were just UNDER 20" tip to tip.
In the case of my buck he was wider than first thought, with my friend, there was "ground shrinkage" as the horns were 3" on either side of the ears, which is how he judged the buck, thinking 6" of air plus 24" of ears=30" buck when in fact it was a 26" rack.
Hope some of this helps.