Key points
- Rule of 31: exit board = oil pattern length (in feet) − 31. A 42-foot pattern gives board 11.
- Length: short up to 36 feet, medium from 37 to 43, long from 44.
- Ratio = oil in the middle ÷ oil on the outside. The higher it is, the more forgiving the lane.
- Rough benchmarks: 3:1 or less for a sport pattern, more than 5:1 for a house shot.
What is the rule of 31?
The rule of 31 is a widely used guideline for choosing your line. It gives the ideal exit board, in other words the point where the ball should leave the oiled area and start hooking towards the pocket (the breakpoint).
Exit board = oil pattern length in feet − 31.
With a 40-foot pattern, the ball should exit around board 9; with 44 feet, around board 13. Boards are counted from the edge of the lane on the side of your bowling hand: from the right for a right-hander, from the left for a left-hander. If the pattern is given in metres, the tool converts it automatically (1 foot = 0.3048 m).
| Length | Exit board | Category |
|---|---|---|
| 35 feet (10.7 m) | 4 | Short |
| 38 feet (11.6 m) | 7 | Medium |
| 40 feet (12.2 m) | 9 | Medium |
| 42 feet (12.8 m) | 11 | Medium |
| 45 feet (13.7 m) | 14 | Long |
This rule is a starting point, not an absolute truth. It works less well on very short or very long patterns, and the ideal line changes over the course of a game as the oil moves. Watch how your ball reacts and adjust using the 2-for-1 rule.
Short, medium or long oil patterns
- Short (36 feet or less): the ball leaves the oil early and hooks quickly. Bowlers tend to play straighter and closer to the outside, with a less aggressive ball.
- Medium (37 to 43 feet): the most common case, especially for bowling centres' “house” patterns. Several lines are possible.
- Long (44 feet and over): the ball skids for a long time. Bowlers play further inside with an aggressive-surface ball.
The oil pattern ratio
The ratio compares the amount of oil laid down in the middle of the lane with the amount on the outside. A 10:1 ratio means there is ten times more oil in the middle than on the edges: a ball thrown too far outside hits a dry area that brings it back towards the pocket. This is the principle behind “house” patterns, which are very forgiving and used by bowling centres for recreational bowling and leagues.
By contrast, a sport pattern (ratio of 3:1 or less) is almost flat: the lane no longer forgives mistakes and accuracy makes the difference. Competitions use this type of pattern. In between, intermediate ratios offer a compromise. These categories are only a guide: the pattern sheets published by centres and organisers give the exact figures.
To learn all about lane machines, oil volumes and types of pattern, read our guide to bowling lane oil patterns.
Frequently asked questions
How does the rule of 31 work in bowling?
Subtract 31 from the oil pattern length in feet to get the board where the ball should leave the oil. For a 42-foot pattern, aim for an exit around board 11.
How long is a house shot?
Bowling centres' house patterns are most often between 38 and 42 feet long (about 11.6 to 12.8 m), with a high ratio that makes them forgiving.
What is an oil pattern ratio?
It is the ratio between the amount of oil in the middle of the lane and the amount on the outside. A high ratio (more than 5:1) makes the lane forgiving; a low ratio (3:1 or less) is typical of the sport patterns used in competitions.
How can I find out the oil pattern at my bowling centre?
Ask at the front desk or the technical manager: many centres display the name and length of the pattern in use, especially on league nights.