How to measure green speed without a Stimpmeter

You can measure green speed without a Stimpmeter by timing a rolling ball. Roll a ball across a flat part of the green and time it from about a foot after it leaves the putter until it stops. Measure how far it rolled in that time. Then:

Stimp (feet) ≈ 9 × time² ÷ distance, with time in seconds and distance in feet.

A ball that rolls 10 feet in 3.3 seconds gives 9 × 3.3² ÷ 10 = 9.8, so a Stimp of about 10. Do it once in each direction and combine the two (see below) to cancel out slope.

This works because of the physics behind the Stimpmeter itself, which we'll explain first. Then there are three methods, from rough to precise, and a table of what the numbers mean for how much your putts break.

What a Stimp number actually measures

A Stimpmeter is a 36-inch grooved ramp. You lift it until the ball releases from a notch, about 20 degrees, and the ball leaves the bottom at a fixed speed of roughly 6 feet per second (1.83 m/s). The green's speed is how far the ball rolls on a flat part of the green, in feet. A 10 means it rolled 10 feet.

That's the only job of the ramp: to launch every ball at the same speed. Once a ball is rolling, the green slows it down at a steady rate, its deceleration. A fast green slows it gently, and a slow green slows it hard. Every Stimp reading is really a measure of that deceleration:

• Stimp = (launch speed)² ÷ (2 × deceleration)

So if you can measure the deceleration some other way, you don't need the ramp. Any ball, rolled at any speed, slows down at the same rate on the same green. That's the idea behind all three methods below.

Method 1: the stopwatch formula

A ball slowing at a steady rate covers distance d in time t with deceleration 2*d* ÷ t². Put that into the Stimp equation with the Stimpmeter's launch speed and the constants collapse to:

• Stimp ≈ 9 × t² ÷ d (feet and seconds)
• In metres: Stimp in feet ≈ 2.74 × t² ÷ d, with d in metres

How to do it

1. Find the flattest part of the practice green you can. On a slope, the ball's speed is changed by gravity, not just the grass.
2. Putt a ball 8 to 15 feet at a gentle pace, straight along a line you can measure.
3. Start the stopwatch once the ball is truly rolling, about a foot after contact, not at impact. For the first few inches a putted ball skids, and that throws off the reading. Mark where you started the clock with a tee.
4. Stop the watch when the ball stops completely.
5. Measure from the tee to the ball. Pace it if you know your step length, or use a tape.
6. Work it out with the formula.

Worked example

Notice it runs the "wrong" way at first glance: over the same 10 feet, the ball on the slow green takes less time. On a slow green you have to hit it harder, and it stops fast.

How accurate is it?

Stimp goes with time squared, so timing errors double. Being 0.1 seconds off on a 3.3-second roll is 3% on time and 6% on Stimp: about ±0.6 at Stimp 10. Hand timing is usually worse than that. Average three rolls and you'll be within about half a Stimp, which is enough to tell a 9 from an 11. That's the difference that matters for how much a putt breaks.

Method 2: make your own ramp

If you'd rather measure the old-fashioned way, you can copy the Stimpmeter:

• A straight 36-inch length of aluminium angle or a V-shaped channel.
• Mark a point 30 inches from the bottom end. That's where the ball starts.
• Lift the top end slowly until the ball starts to roll, which should happen at about 20 degrees.

The catch is that a homemade ramp won't launch the ball at exactly the Stimpmeter's speed. A different groove shape or surface changes how the ball rolls down it. Calibrate it once on a green whose Stimp you know, for example on a day the club posts the reading. If your ramp gives 11 feet on a posted 10, multiply your readings by 10/11 from then on.

Then follow the USGA procedure:

1. Roll three balls in one direction. They should finish within about 8 inches of each other. If they don't, find a flatter spot.
2. Roll three balls back the other way, from where the first three finished.
3. Average each direction.

If the two averages are within about 18 inches, the spot is flat enough. Use the correction below either way.

Method 3: one rolled ball, tracked by your phone

The two methods above are really about measuring deceleration by hand. A phone can measure it directly. Plumb Bob tracks a rolling ball with the iPhone camera. You roll any ball 8 to 15 feet on the green, and the app follows it as it slows and turns that deceleration into a Stimp reading. Roll one back the other way and it combines the two, so the slope cancels out. Your reads then use that speed.

Correcting for slope: roll both ways

No practice green is perfectly flat. Rolling uphill, gravity slows the ball down and the green reads slow. Rolling downhill, gravity pushes it along and the green reads fast. The fix is to roll in both directions and combine them with the Brede formula, which the USGA recommends for sloped greens:

• True Stimp = 2 × up × down ÷ (up + down)

For example, 8.5 uphill and 11.5 downhill gives 2 × 8.5 × 11.5 ÷ 20 = 9.8, not the 10.0 you'd get from a simple average. The formula works just as well for the stopwatch method: work out a Stimp in each direction first, then combine them. (It's exact because the uphill and downhill gravity effects cancel perfectly in the harmonic mean.)

What the numbers mean

Speed matters because faster greens break more. On a faster green the ball is rolling more slowly for longer, so the slope has more time to turn it. We ran a 10-foot putt across a 2% side slope through Plumb Bob's putt simulator, which models a ball rolling over a slope with the green's deceleration:

Same putt, same slope: over 50% more break on the tour-speed green than the slow one. If your reads keep missing on the low side, the green is probably quicker than you think. Speed also changes how hard to hit each putt: see how hard to hit a putt.

FAQ

Can I measure green speed with a phone?

Yes. Either time a rolled ball with the stopwatch and use Stimp ≈ 9 × t² ÷ d, or use an app like Plumb Bob that tracks the ball with the camera and measures the Stimp directly. Roll once in each direction to cancel out slope.

What is a good Stimp reading?

For most public courses, 8 to 9 is normal. Private clubs often run 10 to 11, tour events 12 to 13, and major championships 14 or more.

How do you measure green speed on a sloped green?

Roll in both directions, straight up and down the slope, and combine the two readings with the Brede formula: 2 × up × down ÷ (up + down).

Why do my readings vary so much?

Usually slope, a skidding start or grain. Roll on the flattest spot, start measuring once the ball is rolling, and average several rolls in each direction.

Do faster greens break more?

Yes. A faster green slows the ball more gently, so it spends longer rolling slowly across the slope and turns more. A 10-foot putt on a 2% slope breaks about 50% more at Stimp 12 than at Stimp 8 (13.3 inches against 8.7).