UNDERSTAND / LINE + PACE + SLOPE
The hole is 4.25 inches.
Your usable target often isn’t.
Start line chooses a route. Pace changes that route and changes how much of the cup can actually capture the ball. Use the model to see the tradeoff, then go roll real putts.
Line, pace and slope decide how much hole you have.
Change the green beneath the ball and the roll recalculates continuously. The magnified cup shows the remaining capture width from the ball's actual arrival speed, offset and local grade.
Start line can be set here—or carried in from the Putter Fit Lab.
At the flat 10-foot baseline, the ball reaches the cup at about 1.59 mph, leaving roughly 3.20 inches — 75% — of effective capture width.
What “effective hole size” actually means.
The cup never physically changes. “Effective width” is the band across the 4.25-inch hole within which a ball arriving at a particular speed can still be captured by the hole model. Faster entry leaves less margin for lateral error.
Speed and impact offset work together.
Holmes modeled the interaction between a rolling golf ball and the hole. Penner later used a close parabolic fit to Holmes’ capture boundary. For a level green, the model’s maximum capturable speed falls as the ball crosses farther from the center of the cup.
The tool inverts that relationship to display the effective capture width at the ball’s measured entry speed.
The capture condition changes slightly with grade.
Penner also introduced a small-slope correction to Holmes’ capture model. In this tool, that correction is applied using the signed grade along the ball’s actual arrival direction.
That correction is modest. The much larger practical effect of slope is usually that it changes the ball’s speed and direction before it reaches the hole.
Stimp sets resistance. Gravity bends the path.
- The selected Stimp is converted to rolling resistance using the standard Stimpmeter release speed used in Penner’s model.
- The pace control solves for a launch speed that would stop at the selected level-green reference distance.
- The ball is then integrated through time on the selected two-axis plane. Rolling resistance acts opposite motion; gravity acts downhill.
- At the first intersection with the 4.25-inch rim, the model records entry speed, heading, offset and local travel grade.
- Those values are passed into the capture test.
This assumes the ball is already in pure roll and the green is one constant plane. Real putts include skid, grass variation, grain, moisture, footprints and other local effects.
It is a reference, not a commandment.
“18 inches past” is convenient language, but it does not correspond to one universal entry speed. On a slope, the same desired finishing distance can require very different speeds at the front of the hole.
That is why this lab exposes both the planned pace and the resulting entry speed instead of declaring one “correct” distance past the hole.
Physics helps you make a smarter decision. It does not make the decision.
A model can show the consequence of a chosen line, speed and planar slope. It cannot see the exact grass in front of you, feel your touch that day, understand match context, or decide how much comeback risk you are willing to accept.
- You still have to read the green.
- You still have to choose a pace strategy.
- You still have to start the ball where intended.
- You still have to adapt to grain, moisture and surface imperfections.
- The model’s job is to make the tradeoffs visible before you choose.
Grounded in published putting physics, with the assumptions left visible.
Primary reference: A. R. Penner, “The physics of putting,” Canadian Journal of Physics 80 (2002), building on B. W. Holmes’ hole-capture work. For an applied look at how slope changes entry speed and effective hole size, see Paul Hurrion’s ball-speed-at-hole-entry study. The simulator is an educational numerical implementation of those ideas, not a measurement of a specific real green.