About this site
Last updated: 2026-10-01
The Japanese version of this page is the authoritative text. Other languages are provided for reference; if they differ, the Japanese version prevails.
Site details
| Item | Details |
|---|---|
| Site name | Putt Break Lab |
| URL | https://puttbreaklab.com |
| Operator | GreenEngineer |
| Launched | 2026-09-27 |
| Contact | Contact form |
What this site is for
The purpose of this site is to provide tools and articles that check golfers' instincts against physics.
"It's downhill, so it will run out." "It's cold, so the ball won't go." These instincts are usually right. What they rarely give you is how much — that is hard to turn into a number from experience alone. This site solves the equations of motion numerically to put a concrete figure on that "how much".
Everything is computed in your own browser; the numbers you type are never sent to a server.
About the operator
My name is GreenEngineer.
- 20 years of golf, average score 90
- 20 years as an engineer
I am neither a professional nor a scratch player. That is precisely why I keep running into moments where something I thought I understood by feel turns out, once it is a number, to be far bigger — or far smaller — than expected. That is where this site started.
Technical background
I have spent about 20 years in manufacturing developing software for numerical computation, image processing and control systems. More recently I have worked as a manager across a wider range of areas, including cloud and security.
The methods behind the calculations on this site are the same ones I have used in that work: write down the equations of motion, solve them numerically, and then check the results against measurements.
That said, I have not researched golf ball aerodynamics or green physics professionally. So rather than judging by feel whether a model is right, I validate it against published measurements. The specific figures are set out under "How the calculations work".
Please read what is here as the output of a physics calculation, not as a golf lesson. Nothing on this site is swing instruction or technical coaching.
How the calculations work
The calculations here are not fitted rules of thumb. They are numerical integrations of the equations of motion. The models used, and how they are checked, are set out below.
Putting (Putt Break Calculator)
- Rolling resistance: derived from the Stimpmeter reading. The coefficient is solved numerically so that a ball released at 1.83 m/s rolls exactly the specified number of feet.
- Just after impact: the ball hops, then skids, then rolls purely. When a uniform sphere transitions from sliding to rolling, its speed drops to 5/7 of the sliding speed (implemented in the general form including restitution). That phase takes up roughly 20% of the distance before true rolling begins, which is why a putt barely breaks early on.
- Holing out: the maximum speed at which the ball can still drop instead of lipping out is derived from the geometry. Straight over the centre of the cup it is about 1.63 m/s.
- Slope: treated as a uniform plane at the average gradient, with the downslope component of gravity added.
Shot distance (Carry Range Finder)
- Air density: obtained for moist air from temperature, altitude, pressure and humidity, using the barometric formula of the International Standard Atmosphere together with the Tetens saturation vapour pressure formula.
- Ball flight: the equations of motion including gravity, drag and Magnus lift are integrated with fourth-order Runge–Kutta at a 2 ms time step.
- Aerodynamic coefficients: drag and lift coefficients are given as functions of the spin ratio S = ωr/v. The functional form follows the classic work on golf ball aerodynamics, while the coefficients themselves are calibrated to reproduce published launch-monitor averages.
- How calibration works: for each club, the ball speed that produces exactly the carry you entered under baseline conditions is solved backwards, then that same ball speed is flown again under the day's conditions. Because the result is a difference, errors in the absolute aerodynamic coefficients largely cancel.
Validation
The model's output is continuously checked against published measurements. This is not a matter of displaying figures taken from papers — it checks whether an independent calculation agrees with them.
| Check | Calculated | Published figure |
|---|---|---|
| Driver apex | 29.0 m | about 29 m |
| Driver descent angle | 39° | about 38° |
| Driver hang time | 6.38 s | about 6.3 s |
| Effect of a headwind | about 1 yard per mph | same (rule of thumb) |
| Effect of altitude | 1.0–1.3% per 1000 ft | about 1–2% per 1000 ft |
| Capture speed at the cup | 1.63 m/s | 1.63 m/s |
There are 65 automated tests covering these and other physical properties.
Main references
- B. W. Holmes, "Putting: How a golf ball and hole interact", American Journal of Physics, 59(2), 1991 — holing-out condition
- P. W. Bearman, J. K. Harvey, "Golf ball aerodynamics", Aeronautical Quarterly, 27(2), 1976 — drag and lift on a spinning sphere
- Dave Pelz, Dave Pelz's Putting Bible, 2000 — proportion of the skid phase
- The International Standard Atmosphere (ISA) barometric formula and the Tetens formula — air density
- Tour averages published by launch-monitor manufacturers — ball-flight calibration and validation
Advertising
This site plans to carry advertising to cover the cost of running it. No advertising is being shown at present. This page will be updated when that changes.
Once advertising starts, providers may use cookies in order to show ads matched to your interests. For what is collected and how to opt out, please see the Privacy Policy.
Disclaimers
About the results
The results on this site are estimates based on a particular set of physical models. They do not guarantee what will happen in actual play.
Real shots and putts are affected by the following, none of which is part of the calculation.
- Complex undulation in the green, turf condition, dew or rain
- Variation in your swing or stroke, and where you strike the ball
- Differences in the aerodynamics of different ball models
- Wind that changes with height (wind shear), and gusts
- Roll after landing (the Carry Range Finder computes carry only)
No responsibility is accepted for decisions made on the basis of these results, or for their outcome.
About accuracy
While every effort is made to keep the information here correct, its completeness and currency are not guaranteed. Results may change without notice as models are improved or errors are corrected.
Health and safety
This site does not offer swing instruction or advice on how to use your body. No responsibility is accepted for injury or accident during play. If you have any concern about your health or physical condition, please consult a qualified professional.
External links
No responsibility is accepted for the content of any website you reach from here.
Continuity of service
The content of this site may be changed, suspended or discontinued without notice.
Copyright
Copyright in the text, figures and programs published on this site belongs to GreenEngineer. For use beyond the scope of quotation, please get in touch through the contact form.
Questions about the site, and corrections, are welcome through the contact form.