What is a green book?

The short answer

A green book is a pocket-size booklet containing a map of every green on a golf course, showing which way each one slopes and how a putt will break. Tour players carry them. Most also map the hole itself — the fairway, bunkers, water and yardages — which is why you'll sometimes hear them called yardage books.

The point is simple: standing over a putt, you can see the slope you cannot feel.

What's inside one

• Slope percentage — how steep the green is, hole by hole. Around 2% is a gentle tilt; 5% and above is severe.
• Break arrows — each arrow points downhill, the direction a ball will roll. Longer arrow, steeper ground.
• Elevation contours — lines joining points of equal height. Lines close together mean a steep slope; far apart means flat.
• A depth grid — usually in 5-yard bands, so you can judge how far on the green the pin is.
• The hole map — fairway, bunkers, water, trees and yardages from each tee.
• Carry distances and elevation change — how far to clear trouble, and whether the green sits above or below you.

How to actually read one

Find your pin position on the green map, then look at the arrows around it. They point where the ball wants to go, so your putt will break that way. Check the contour lines between your ball and the hole: if you cross several, the putt is travelling over real slope and will break more than it looks. The percentage tells you how much.

Two habits make the difference. Read the whole path, not just the area by the hole — most of the break happens where the ball is still moving quickly. And treat the book as a second opinion: it shows general tilt and tiers, not the exact break on the day. Grain, wind and a freshly-cut green all still matter. Trust your own read; use the book to catch what your eyes missed.

Are green books allowed in competition?

Rule 4.3 limits the size and scale of green-reading material rather than banning it. The two limits are set out in its Clarification 4.3a/1: no putting green may be drawn at more than 3/8 inch to 5 yards, and the book or sheet carrying it may be no larger than 4¼ × 7 inches. The books here are palm-size at 3.5×5″, and every green is drawn at 1:480 or smaller — the largest of them prints at about 1:500, roughly 4% inside the scale cap.

Three honest caveats. Conformance is not guaranteed for every hole. A Committee can also restrict or prohibit green-reading material whatever its size, using Model Local Rule G-11 (you may use only a book the Committee has approved) or G-12 (no using print to read the line while your ball is on the green). And the Committee running your competition has the final say regardless. Ask them before you play — many events allow these books, and some don't.

Why the ones here are different

Most commercial green books are sold one course at a time, and some cost more than a junior can easily pay. These are made from public data — OpenStreetMap for the shapes, public-domain USGS 3DEP LiDAR for the elevation, and the published scorecard for par and yardage. Printed and bound by hand.

Request a green book

Or look at every course with a book so far — each has its own page with the scorecard and a real page from the book.