The 30° Rule
by Dr. Dave, from the book: “The Illustrated Principles of Pool and Billiards”
billiards.colostate.edu
If you let one finger stay,
The other finger points the way.
Peace.
If you don’t know the 30º rule yet, learning it can truly transform your game. The 30º rule helps you predict the path of
the cue ball after impact with an object ball. This is a very important skill to have for helping you prevent scratches, plan
break-up and avoidance shots, and execute carom and billiards shots. It is also critical in being able to play precision
position ... the skill that separates the great players from the good ones.
When the cue ball is rolling when it hits the object ball, and when the cut angle is between a 1/4-ball and 3/4-ball
hit, the cue ball’s path will be deflected by approximately 30°.
fast
medium
slow
30° deflected angle
cue ball deflection angle
40º
the cue ball’s path
is deflected by 30°
30º
20º
wide margin of error
10º
aiming
line
half-ball hit
1/2
1/4
3/4
1
ball-hit fraction
You can use a relaxed but firm peace sign (V-sign) to visualize and apply the 30º rule:
the faster the shot,
the more you shift your hand
along the tangent line
deflected
cue ball
path
original
(incoming)
cue ball
path
tangent
line
fast
30°
30°
slow
30º
For more information, see the April-July '04 and Feb-June '05 instructional articles
and the following video demonstrations on the website:
normal video
NV B.66 − The 30-degree rule, from VEPS I
NV B.75 − 30-degree rule natural-angle examples, from VEPS III
normal video