You don't have to know the equities of every single combination of hands, dresturn.
In general, people memorize the more common situations like (stolen from HoH):
Higher pair vs lower pair is 4.5:1
Pair vs overcards is 55:45 or 1.2:1
Pair vs lower cards is 5:1
Pair vs higher and lower cards is 5:2 or 1.5:1
Two higher cards vs two lower cards is 5:3 or 1.7:1
Here's a nice article by our very own Fredrik Paulsson on equity: Poker: Equity