How to plumb bob a putt (and when it lies to you)

To plumb bob a putt: stand a few feet behind your ball on the line to the hole. Hold your putter lightly at the top of the grip so it hangs straight down, and close your non-dominant eye. Line the lower part of the shaft up with your ball, then look up the shaft. The hole appears on the side the putt breaks toward. If the hole is to the right of the shaft, the putt breaks left to right. If the shaft covers the hole, it's straight.

That's the technique golfers have used for a century. It's also widely misunderstood, and it's often wrong about how much a putt breaks. Below is the step-by-step version, the geometry of why it works at all, and the putts where it lets you down, with numbers from the same physics our app uses to read greens.

How to plumb bob, step by step

1. Find your dominant eye

Plumb bobbing only works with one eye. Hold your arm out, make a small circle with your thumb and forefinger, and frame a distant object with both eyes open. Close your left eye. If the object stays in the circle, you're right-eye dominant. If it jumps out, you're left-eye dominant. Keep the dominant eye open for every read.

2. Stand behind the ball, on the line

Stand two to four feet behind the ball, on the extension of the line from the hole through the ball. Stand naturally with your weight even. Don't try to straighten your body against the slope: as you'll see below, the lean the slope puts in your stance is what makes the method work.

3. Hang the shaft

Hold the putter between your thumb and forefinger at the top of the grip, at arm's length, and let it hang freely. A putter doesn't always hang perfectly vertical, because the head's weight sits off-centre. Turn the toe toward or away from the hole until the shaft looks straight, and use that orientation every time.

4. Cover the ball

With your dominant eye only, move the putter sideways until the lower part of the shaft covers the ball.

5. Look up the shaft to the hole

Without moving the putter, look up the shaft to the hole.

• Hole to the right of the shaft: the putt breaks left to right.
• Hole to the left of the shaft: the putt breaks right to left.
• Shaft covers the hole: the putt is straight, or the slope under you matches the slope at the hole.

The further the hole sits from the shaft, the more slope there is where you're standing. That's the most the plumb bob tells you. It doesn't tell you where to aim.

Why plumb bobbing works (the geometry)

A lot of golfers think the hanging shaft somehow "shows" the slope. It doesn't. The shaft only marks a vertical line. The information comes from your body.

When you stand on a side slope, you naturally stand a little square to the ground rather than perfectly upright. Your feet are on the slope, so your head ends up slightly downhill of the line. Now sight past the vertical shaft to the ball: the vertical plane through your eye and the ball runs uphill of the hole as it goes past the ball. So the hole appears on the low side of the shaft, which is the side the putt breaks toward.

That also shows how small the effect is. Here are the numbers for a 2% side slope (the typical slope around a hole location), with eyes about 1.6 m (5 ft 3 in) above the ground and standing 1.2 m (4 ft) behind the ball:

• Your eye sits about 3 cm (1¼ in) downhill of the line.
• At a 10-foot putt, the hole appears about 3 inches off the shaft.
• At 20 feet, it appears about 6 inches off.

Now compare that with how much the putt actually breaks. We ran the same putt through Plumb Bob's putt simulator, which rolls a ball over the slope at a given green speed (Stimp 10, with the ball dying about 17 inches past the hole):

You can try any putt in our putt break calculator, which shows both numbers. Two things stand out:

1. The plumb bob gets direction right but underplays the amount by a factor of three to five. Aiming where the shaft points under-reads nearly every putt. That's the classic plumb-bob miss: on the low side.
2. It can't see speed or grade. The plumb bob shows the same thing for the uphill and downhill 10-footer, but the downhill putt needs almost twice the break. It shows the same on a Stimp 8 green and a Stimp 12 green too, where the 10-footer needs 8.7 and 13.3 inches of break respectively.

When plumb bobbing lies to you

The plumb bob reads the slope under your feet, not the slope under the ball's path. That's fine when the green is one tilted plane. It's wrong on these putts:

Double breakers

If the green falls right near you and left near the hole, the plumb bob reports the slope at your feet: right. The ball spends its slow, break-heavy final few feet on the left-breaking section. That's the part that matters most. Walk to the hole and read the last third of the putt from there.

Standing on a different slope from the line

Stand on a ridge, in a swale or on the fringe beside the line, and the plumb bob reads that ground. Always stand on the extension of the actual putting line, not just "behind the ball".

Uphill and downhill putts

On a putt that runs straight up or down the fall line, there's no side slope, so the plumb bob correctly shows straight. But on a putt that's slightly off the fall line, the side slope is small while the break can still be large, especially downhill. The shaft will show almost nothing on a putt that breaks two cups.

A putter that doesn't hang straight

A heel-shafted blade hangs at a slight angle, and a face-balanced mallet hangs differently again. If the shaft isn't truly vertical, every read is biased the same way. Test it against a door frame or a flagstick before relying on it.

Standing up straight

If you deliberately stand upright against the slope, you remove the tilt that makes the method work. Then the shaft will say "straight" on every putt.

So is plumb bobbing worth doing?

Yes, as a direction check, especially on short putts where you can't tell which way the green tilts. It's quick, it's legal in every competition, and it's better than guessing. Just don't use it to decide how much to play. For that you need the slope along the whole putt, the grade and the green speed.

The best way to build that feel is to check your reads against the real thing. That's why we built Plumb Bob. You mark your ball, walk to the hole while the camera maps the slope of the whole line, then stand behind the ball and hold the phone up. The phone knows exactly where vertical is, so the plumb line is perfect. It rolls test putts over the measured slope at your green speed and draws the line that drops, with the aim point in inches. Do that a few dozen times on the practice green and you'll find out how much you under-read, and on which putts. (Nearly everyone does: see why you miss putts on the low side.)

(A device read isn't allowed in competition, though. See are green reading apps legal? Plumb bobbing with your putter is.)

FAQ

Which side does the putt break when plumb bobbing?

Toward the side the hole appears on. If the hole is to the left of the hanging shaft, the putt breaks right to left. If it's to the right, it breaks left to right.

Which eye do you use to plumb bob?

Your dominant eye, with the other one closed. Find it by framing a distant object between your thumb and forefinger with both eyes open, then closing one eye at a time. The eye that keeps the object framed is dominant.

Does plumb bobbing actually work?

For direction, mostly yes, as long as the green is one consistent slope and you stand on the line. It underplays how much the putt breaks, often by a factor of three or more, and it can't account for green speed, uphill or downhill, or double breaks.

Do tour players plumb bob?

Some do, often as a quick check alongside reading with their feet and from the low side. More tour players now use AimPoint, which reads slope through the feet.

Is plumb bobbing legal?

Yes. It uses only your putter and your eyes, so it's allowed in every competition. Using a phone or a level to read the slope during a round is not (Rule 4.3).