How to Calculate the Difficulty of a Golf Course And Slope Rating
Golf is a game of jargon. Number of holes to a course; the number of strokes to each hole; handicaps, birdies, par, albatrosses; scratch, bogie, slope rating, eagle, ace...and so it goes on! As well as all its jargon, however, golf is also a game of numbers and of rules.
Like all games, golf needs regulations to ensure that everybody is on a level playing field, so to speak.
Not that many golf courses are level playing fields. But we'll get to that shortly.
Play a Round Anywhere
Golf is a standardized game.
Whether you are playing at St. Andrews, Augusta, or the back nine at the Denfield Golf Course on the South Island of New Zealand, golf’s rules, standards and, above all, its handicap system, allow players of all abilities to compete on an equal footing.
Golf’s handicap system ensures that even the most hopeless hacker has at least a chance of beating a top player - Tiger Woods, for instance - on any course in the world.
Course rating is one of the foundations of the golfing handicap system. Without course rating, players wouldn't be able to post scores or maintain a handicap index.
Course rating assigns a numerical value to the difficulty of a golf course for a scratch player. Scratch players are defined as:
- A male scratch player is a golfer who can hit tee shots approximately 250 yards long and reach a 470-yard hole in two shots at sea level.
- A female scratch player, on the other hand, can hit an average of 210 yards off the tee and reach a 400-yard hole in two shots at sea level.
The course rating number is calculated by measuring dozens of different factors for each tee, on every hole of a golf course. This means that thousands of values have to be collected and collated before the course’s rating can be computed.
Course rating is done by a team from the local Golf Association. Teams usually consist of an experienced leader, and volunteers who have been trained according to the rules set down by the United States Golf Association.
Most golf courses are rated every 10 years. But ratings may be done more frequently if renovations or significant changes have been made to a particular hole or an entire golf course.
Rating a Course
A course rating team is usually composed of four to six members. The team will divide up into several groups who will then “leapfrog” around the course, evaluating alternate tees.
The team collects and collates data from each tee. They will then play an informal round on the entire course, to double check the observations that they have made from a playing standpoint.
Many Many Features
The features of a golf course that the course rating team have to measure include:
- Shape and size of contours.
- Dimensions of bunkers.
- Height and layout of hills and hummocks.
- Size of the putting greens.
- Contours and shapes of the greens.
- Distance to out-of-bounds and water hazards.
- Fairway length.
These days, GPS units have made the job of working out distances and heights on a golf course a relatively simple and fast procedure.
Before the advent of GPS and ranging lasers, course rating involved long hours with tape measures, and even pieces of knotted rope, to measure distances, heights, widths and elevations.
Thousands of Figures
There are generally a set of 26 evaluations applied to each set of tees on each individual hole.
For example, on a hole that comprises five shots, each one of those five shots will be ranged for distance and width, and its specific features (bunkers, obstacles, water hazards, etc) evaluated.
On average, around 2500 values will be used to calculate the course difficulty.
In order to work out the speed of a putting green, a simple tool called a Stimpmeter is used.
This consists of a length of aluminium channel with a small depression in it to hold the ball. As the channel is raised to an incline of 20°, gravity releases the ball which then rolls down the channel and across the green.
Three balls are rolled in each direction from a set point in the center of the green. The distance that the balls travel is measured, and the average is used to calculate the speed of the green.
Plotting the Graph
When all of the calculations, evaluations and number crunching is done, a course rating team ends up with two different numbers:
- Expected average score for a scratch golfer.
- The expected average score for a bogey golfer.
The Scratch golfers score becomes the Course Rating. This is expressed as a number to one decimal place: say 69.3.
Both the scratch score and the bogey score are then plotted on a graph, with the scratch golfers score on the left hand axis and bogey golfers score on the right hand axis.
Both the left and right axes are divided up in increments of five, from fifty to one hundred and twenty.
Along the bottom of the graph is the Handicap Index, marked in increments of 2, from zero to twenty.
Now for Some Algebra
If you cast your mind back to your High School algebra classes (sorry...but this bit is important!) you will remember that the slope of a line is a function of its length and its height.
By subtracting the bogey rating from the course rating, then multiplying by either 5.381 for men, or 4.24 for women, you arrive at the course’s Slope Rate. Easy!
The slope rating doesn't necessarily tell you how hard or easy a particular course is. But it does tell you how much more difficult it is for a bogey golfer compared to a scratch golfer.
Slope ratings can range from a very easy 55 (easy, that is, for a bogey golfer) to a very difficult 155. The average Slope Rate for golf courses is around 113.
Well...that wasn’t so hard now, was it?
Golf, like any other game, is meant to be fun. Of course it is important to have all the regulations and handicaps figured out in such a way that it makes the game fair for every player.
But it's easy to get tangled up with convoluted figures and complex calculations. So why not let the boffins compute the slope rates, and figure out the course ratings.
All you need to do is just go for a walk, and tap some little white balls around with various different-shaped sticks. Fore!
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Not sure where to begin? Let us help! Every good golfer needs a few staples before getting started. Let’s take a look at some of the articles we have for you.
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