The Stimp value tells the app how fast the greens are rolling today. Getting it right does more for line accuracy than any other setting.
Green speed varies by course, country and season. Expect slower greens after rain and in winter, faster ones in dry summer conditions.
Where to find today's number
Ask the greenkeeper before your round. They measure it daily.
Check the pro shop or starter's desk. Many clubs post the daily green speed.
Check the scorecard or course app. Some clubs publish it there.
No number available?
Start with 9 and calibrate. Pick a putt with some break in it, because a straight putt tells you nothing. Aim at the line the app draws, play it, and watch which side you miss on:
Missed high, above the hole: the app is showing more break than the green has. Lower the Stimp.
Missed low, below the hole: it is showing too little. Raise it.
Most players lock this in within three or four putts.
Quick reference
7 to 8 slow, after rain or in winter. 9 to 10 average club conditions. 11 to 12 fast and well prepared. 13 plus tournament speed.