The payouts for the big and small bets are 1 to 1. For a bet to qualify as small, the result needs to be between four and ten, and for a bet to be termed as big, it needs to be between eleven and seventeen. You also have the option to bet on whether the total of the three dice will be small or big. As you place the bets, you will have the payout amounts displayed on the betting squares. The payout on each of the bets you make will be different, and this is because of the probability of occurrence of each score.
As for three and eighteen, they are covered by triple 1 and triple 6 respectively. This is the easiest bet in the game where you predict the total of the three dice.