calcpace

https://github.com/0jonjo/calcpace

Ruby gem for runners: pace, time, and distance calculations, unit conversions (30+ units), race time predictions (Riegel, Cameron, personal Riegel exponent, and Tanda marathon from training volume), GPS track analysis (Haversine, elevation gain, per-km splits, Minetti grade-adjusted pace), heat, humidity, and altitude adjustments, age grading (2025 road tables), VO2max estimation (Daniels & Gilbert) with FRIEND age/sex norms, and personalized training zones (Daniels paces & Karvonen heart-rate zones).