No need for a web site.
35' lines, 12 laps per half-mile.
42'; 10 laps,
52.5'; 8 laps,
60'; 7 laps,
70'; 6 laps.
Divide the half mile time into 1800 and you have MPH.
For a full mile, use 3600.
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30' is half of 60', so a half mile equals 14 laps.