What is the 30° rule?

The 30° rule states that for a rolling-CB shot, over a wide range of cut angles, between a 1/4-ball and 3/4-ball hit, the CB will deflect by very close to 30° from its original direction after hitting the OB. If you want to be more precise, the angle is a little more (about 34°) closer to a 1/2-ball hit and a little less (about 27°) closer to a 1/4-ball or 3/4-ball hit. The rule is described and illustrated in the following videos:

The Dr. Dave peace-sign technique is very useful in applying the 30° rule. The 30° rule angle templates can be useful to help you calibrate your V-sign. If you want to know how the CB path varies with speed and how to account for this, see speed effects. And if you want to see how numbers change a little with typical pool equipment conditions, see “Rolling Cue Ball Deflection Angle Approximations” (BD, November, 2011).

Here a video demonstrations showing examples of how the 30° rule can be used in different shot situations:

and here are some others:

Here’s a convenient 1-page summary resource page summarizing all of the important points of the 30° rule, and here’s a useful handout covering advanced topics.

For more info, see “The 30° rule: Part I – the basics” (BD, April, 2004) and where the CB goes for different cases.

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