Running pace & race estimates

Pace & splits: choose whether to calculate pace from a distance and time, or finish time from a distance and pace. Time accepts mm:ss or h:mm:ss; pace uses m:ss per selected km or mile. Units apply to the entered numbers; changing km/mi reinterprets them rather than converting the inputs. Other units are available in the result.

Splits assume constant speed. Set section length under Split settings (default 1 km or mile). The final partial section is included. Total timestamps are rounded to whole seconds first; section times are differences of those timestamps, so they add up to the displayed finish time. Zero-second sections can occur below the display resolution. Values below half a second show < 0:01 outside the split table.

Race estimate

Enter a recent, comparable race distance and time and choose the target. Half marathon is 21.0975 km, marathon 42.195 km, international mile 1.609344 km. Custom distance supports km and miles. Riegel uses T₂ = T₁ × (D₂/D₁)^k; distances are converted to the same unit.

The default exponent 1.06 is a common convention, not a personal calibration. Model settings allow 1–1.3 for sensitivity exploration. Larger exponents give slower times on longer distances and faster times on shorter distances. This range is a calculator setting, not a validated physiological interval. The comparison skips the entered race and chosen target.

This is a model estimate, not a guaranteed finish or a confidence interval. Training, terrain, weather and preparation for the target distance matter. Research on recreational runners found Riegel forecasts especially optimistic for marathons; long-distance and ultramarathon extrapolations need particular care.

Operation and limits

Calculate or Enter runs the active calculator. Editing inputs removes its old result. Reset affects only the active calculator; inputs and active tab are remembered. Distance and section inputs are limited to 10,000 of the selected unit, time/derived pace to 10⁹ seconds, split tables to 500 rows. Increase section length for longer distances; no silent truncation.

Sources

Vickers & Vertosick (2016): recreational runners and Riegel · World Athletics: half marathon · Marathon · NIST: international mile