Betting Unit Size You should think about the type of investor that you are. Are you aggressive or conservative? Are you experienced or a novice? The answers to these questions will help you to determine the size of your typical bet. This is called your betting unit size. We typically recommend that a sports investor bet 1%-3% of their bankroll on each bet. Conservative sports investors (or beginners) should bet 1%-2% on a play. Note that professional’s betting unit sizes are normally in the 1% range.