Here is the whole rule in one line. Take the oil pattern length in feet and subtract 31. That number is the board your ball should be exiting the oil on.
The National Bowling Academy walks through the Rule of 31 and ball motion the same way.
Forty-foot pattern? Forty minus 31 is 9. Get your ball out to the 9 board at the end of the pattern and you are in business.
That is it. That is the famous Rule of 31.
Now the honest part. This is a starting line, not a magic number. It gets you close on the first shot so you are not throwing blind. It does not read the lane for you, and it does not account for your rev rate, your ball, or how much the lane has broken down. We will cover all of that below, because knowing the formula is easy and using it well is where most bowlers trip.
What the Rule of 31 actually is
The Rule of 31 is a shortcut for finding a smart place to send your ball on a lane you have never seen.
Every oil pattern has a length, measured in feet, from the foul line down. Common league patterns run 38 to 42 feet. Sport and PBA patterns can run anywhere from 32 feet up past 45.
The rule says: pattern length minus 31 equals your target exit board. So the ball should be crossing that board right around where the oil ends.
Why 31 and not some other number? It is not a physics constant. It is a rule of thumb that pattern designers and coaches landed on because it lines up the ball’s exit with a spot that, on most patterns, feeds the pocket for a normal hook shape. Think of it as a well-tested average, not a law.
The board it gives you is measured at the end of the pattern, not at the arrows and not at the pins. That distinction matters, and it leads straight into the mistake we see most.
Exit point is not your breakpoint
This is the part almost every article skips, and it is the part that actually helps your game.
The number the Rule of 31 gives you is your exit point. That is the board where your ball leaves the oil and first touches dry lane. It is not your breakpoint.
Your breakpoint is the spot further down the lane where the ball actually stops sliding and makes its move back to the pocket. It sits a few feet past the exit point, because the ball needs a beat on the friction before it changes direction.
So when the Rule of 31 hands you the 9 board on a 40-foot shot, it is telling you where the ball should come out of the oil. The breakpoint, the visible move, happens a little later and usually a board or two further right for a right-hander.
Why should you care? Because if you treat the exit number as your breakpoint, you will read your ball reaction wrong. You will think the ball is hooking too early when it is actually exiting right where it should. Get this straight and every adjustment you make afterward gets sharper.
The Rule of 31 chart
Here is the math done for you across the pattern lengths you will actually see. Exit board is pattern length minus 31.
| Pattern length | Rule of 31 exit board | Where you see it |
|---|---|---|
| 32 ft | 1 | Short sport patterns (Cheetah) |
| 35 ft | 4 | Short house and sport shots |
| 36 ft | 5 | Common short pattern |
| 37 ft | 6 | Shorter house shots |
| 38 ft | 7 | Standard house shot |
| 39 ft | 8 | Standard house shot |
| 40 ft | 9 | The classic house shot |
| 41 ft | 10 | Longer house / medium sport |
| 42 ft | 11 | Long house shot |
| 43 ft | 12 | Medium-long sport (Scorpion) |
| 44 ft | 13 | Long sport patterns |
| 45 ft | 14 | Long sport (Shark territory) |
Read it like this. On a 38-foot house shot, aim to get your ball out to the 7 board at the end of the oil. On a 44-foot sport pattern, that exit board moves in to 13, which means you are playing straighter and closer to the middle. That is the whole point. Longer oil pushes your line inside. Shorter oil lets you get out to the edge.
If you want the pattern length for a specific tournament or animal pattern, we keep a full breakdown on our oil patterns hub.
How to actually use it, step by step
The formula is only useful if you turn it into a shot. Here is the sequence we run on a fresh pattern.
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Get the pattern length. For league, ask the desk or check the house shot sheet. Sport and tournament patterns are posted, usually with the length right in the name or on the sheet. Kegel and PBA pattern sheets list it plainly.
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Do the math. Length minus 31. Write down that exit board.
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Build your line to that board. Pick a target at the arrows and a launch angle that sends your ball through that exit board at the end of the pattern. On a 40-foot shot, a right-hander might stand around 20, target the 10 board at the arrows, and let the ball work out to the 9 at the end.
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Throw it and watch the exit, not the pocket. Did the ball come out of the oil around your target board? Ignore whether you struck for a second. You are checking the exit first.
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Then judge the reaction. If the ball exited where you wanted and still missed, now you adjust. That is the next section.
The Rule of 31 gets you a credible first shot. Everything after that is reading what the lane and your ball tell you.
Where the Rule of 31 breaks down
We promised honest, so here are the places the rule lies to you.
Very short patterns. On a 32 or 35-foot pattern, the exit board sits way out near the gutter. That can work, but it also means tiny misses get punished hard, and a lot of bowlers cannot repeat a shot that close to the edge. The math is right. Your margin is not.
Very long patterns. Past 44 or 45 feet, the number pushes so far inside that a normal hook can not make it back to the pocket in time. The rule assumes a standard ball reaction. On long oil you often need to play even straighter than the number suggests, or throw a weaker ball.
Your rev rate. The Rule of 31 was built around a moderate, tournament-average ball motion. If you are a big rev player, your ball covers more boards, so you may want to exit a board or two inside the number. If you are a low-rev or stroker type, you may need to exit a touch further out to get the same shape. The number is a midpoint, and you live somewhere off that midpoint.
Your ball and surface. A strong solid at 500 grit reads the lane earlier and needs a different exit than a shiny pearl that skids long. Same pattern, same math, different ball, different line. The formula does not know what is in your hand.
Lane breakdown. After a few games the oil moves. Carrydown and breakdown shift where your ball wants to be. The Rule of 31 gives you the fresh-lane starting point. It does not follow the transition. That is on you.
How to adjust off the starting line
Once you have thrown your Rule of 31 shot, you read and move. Quick guide.
Ball hooks too early, leaves the pocket flat or comes up light. The lane has more friction than the number assumed, or your ball is too strong. Move your feet and target left (for a righty) to get the ball further into the oil, or switch to a weaker ball or a smoother surface.
Ball skids too long, hits weak on the right side or misses right. Not enough friction where you are playing, or the ball is too clean. Move right to find the dry, or go to a stronger, earlier-reading ball.
Good pocket, no carry. Your line might be fine and the issue is entry angle or speed. Small moves, not big ones. Do not blow up a decent look chasing one bad rack.
The Rule of 31 is the anchor. Your adjustments are small steps away from it, not a reason to abandon it. If you find yourself six boards off the number and striking, great, the pattern is just built that way. You still started from a smart place instead of a guess.
Frequently Asked Questions
What is the Rule of 31 in bowling?
It is a formula for finding a starting line on any oil pattern. Take the pattern length in feet and subtract 31. The result is the board your ball should exit the oil on. On a 40-foot pattern, 40 minus 31 is 9, so you aim to get the ball out to the 9 board at the end of the oil.
How do I find the oil pattern length?
For league, ask the front desk or check the posted house shot sheet. Most houses run a 38 to 42-foot pattern. For sport and tournament play, the pattern sheet lists the length, and Kegel and PBA sheets show it clearly. The animal patterns each have a set length too.
Does the Rule of 31 work on a house shot?
Yes, and that is where it works best. House shots usually run 38 to 42 feet, which puts the exit board between 7 and 11. House oil also has friendly friction on the outside, so the number lines up with a repeatable pocket line for most bowlers.
Is the exit point the same as the breakpoint?
No, and this trips people up. The Rule of 31 gives you the exit point, the board where the ball leaves the oil. Your breakpoint, the spot where the ball actually makes its move back to the pocket, sits a few feet further down the lane. Read your ball’s exit first, then judge the breakpoint.
Does the Rule of 31 work on sport patterns?
It gives you a starting point, but sport patterns demand more precision and the number gets less forgiving. On short sport patterns the exit board sits near the gutter with little margin. On long ones the number pushes so far inside a normal hook can not recover. Use it to start, then adjust hard.
What board do I target on a 40-foot pattern?
The 9 board at the exit. Forty minus 31 is 9. Build a line that carries your ball out to the 9 board at the end of the oil, then watch the reaction and adjust from there.
10th Frame Final Thoughts
The Rule of 31 is not a secret and it is not a cheat code. It is a smart first guess that keeps you from throwing blind on a lane you have never seen. Pattern length minus 31, exit on that board, then read your ball and move.
The bowlers who get real value out of it are the ones who understand what it gives them, an exit point, not a breakpoint, and who treat the number as a starting line instead of gospel. Start there, watch your reaction, make small moves, and you will find the pocket faster than the person next to you who is out there guessing.
Know the math. Then go read the lane. Stay hungry.
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