The maximum legal weight of a bowling ball is 16 pounds (or 7.27 kilograms). For that reason, a lot of bowlers use 16-pound bowling balls, whether they should or not. If a 17-pound ball was allowed, plenty of those who currently use 16 pounders would move up to 17.
Some of that comes from a bowler's ego. That is, a bowler will think to himself, "I can throw anything, no matter how much it weighs."
Aside from a macho mindset, many bowlers throw the heaviest possible ball because of the conception a heavier ball will knock down more pins more frequently than a lighter ball.
Is Heavier Better?
In general, yes. If a 16-pound ball and a 15-pound ball are thrown at the same speed, the impact of the 16 pounder will be greater. But in that scenario, we're assuming everything except the weight of the ball is equal. When it comes to bowling, very few things are equal.
If you can't comfortably throw a 16-pound ball, you're not going to bowl well and you're going to hurt yourself. If you step down to a 15- or 14-pound ball, your game will improve dramatically, as you'll be able to throw the ball all night without much strain on your body. This also lowers your chance of injury.
Then What's the Best Ball Weight?
There is no universal ball weight that works for everyone. A child has no business using a 16-pound ball, and most adults have no business using an eight-pound ball. In general, the best ball weight for you is the heaviest ball you can comfortably throw for an extended period of time. A ball you can throw with ease for one game doesn't do you much good if you have two more games to bowl. For most adults, this ranges from 14-16 pounds. Kids, teens and young adults, depending on age and strength, will use a ball anywhere from 6-14 pounds.
There's no shame in using a ball lighter than 15 pounds. Would you rather bowl a 170 with a 15-pound ball and feel great the next day, or bowl a 130 with a 16-pound ball and deal with soreness for days afterward? When you throw a ball at the ideal weight for you, you bowl better and avoid injuries.
Determining the Best Ball Weight
Some people say you should get a ball equal to 10% of your body weight (up to the maximum of 16 pounds, of course), which is good as a general guide, but shouldn't be taken as a hard rule. It comes down to comfort. If you can throw a 16-pound ball for five frames before getting tired or sore, you need a lighter ball. If you can throw a 12-pound ball all night with extreme ease, you should get a heavier ball.
Many bowling pro shops will let you try bowling balls of different weights to determine which one is best for you. You can also test for yourself by using house balls of different weights, although it's important to note a house ball will feel heavier than a custom-drilled ball of the same weight. That is, a 14-pound house ball may feel more like a 15- or 16-pound custom-drilled ball. This is due to the perfect grip you have with your own ball making it easier to lift and hold than a house ball that was drilled to fit as many people as it possibly can.