this is from wikipedia
International pool
Classic-style pool balls racked for a game of eight-ball, just before the break shot.
Modern-style pool balls
Pool balls are used to play various pool (pocket billiards) games, such as eight-ball, nine-ball and one-pocket. In North America, they are sometimes referred to simply as "billiard balls" (except among carom players), and in the UK they are commonly referred to as kelly pool or American balls. These balls, used the most widely throughout the world, are considerably smaller than carom billiards balls, slightly larger than British-style pool balls and substantially larger than those for snooker. According to WPA/BCA equipment specifications, the weight may be from 5.5 to 6 oz. (156–170 g) with a diameter of 2.25 in. (57.15 mm), plus or minus 0.005 in. (0.127 mm).[7][8] The balls are numbered and colored as follows:
1. Yellow
2. Blue
3. Red
4. Purple (pink in some ball sets)
5. Orange
6. Green
7. Brown or burgundy (tan in some ball sets)
8. Black
9. Yellow and white
10. Blue and white
11. Red and white
12. Purple and white (pink and white in some ball sets)
13. Orange and white
14. Green and white
15. Brown, or burgundy, and white (tan and white in some ball sets)
• Cue ball, white (sometimes with one or more spots)
Note that balls 1 through 7 are often referred to as solids and 9 through 15 as stripes though there are many other colloquial terms for each suit of balls (highs and lows, etc.). Though it looks similar to the solids, the 8 ball is not considered a solid. Some games such as nine-ball do not distinguish between stripes and solids, but rather use the numbering on the balls to determine which object ball must be pocketed. In other games such as three-ball neither type of marking is of any consequence. In eight-ball, straight pool, and related games, all sixteen balls are employed. In the games of seven-ball, nine-ball, ten-ball and related, only object balls 1 through 7, 9 and 10, respectively (plus the cue ball) are used.
Some balls used in televised pool games are colored differently to make them distinguishable on television monitors. Specifically, the 4 ball is colored pink instead of dark purple, and the 12 is white with a pink stripe, to make it easier to distinguish their color from the black 8 ball, and similarly the 7 and 15 balls use a light tan color instead of a deep brown. The TV is also the genesis of the "measle" cue ball with numerous spots on its surface so that spin placed on it is evident to viewers.
Coin-operated pool tables such as those found at bars historically have often used either a larger ("grapefruit") or denser ("rock", typically ceramic) cue ball, such that its extra weight makes it easy for the cue ball return mechanism to separate it from object balls (which are captured until the game ends and the table is paid again for another game) so that the cue ball can be returned for further play, should it be accidentally pocketed. Rarely in the US, some pool tables use a smaller cue ball instead. Modern tables usually employ a magnetic ball of regulation or near-regulation size and weight, since players have rightly complained for many decades that the heavy and often over-sized cue balls do not "play" correctly
..................so a cue ball can weight from 156 grams to 170 grams
hope this is helpfull