Pick what you want to work out, fill in the other two, and get the answer in minutes per km and per mile, plus speed. Then plan your splits and see what your time predicts for other race distances.
Most personal bests come from a "negative split": running the second half slightly faster than the first. Slide to shift effort from start to finish. The total time stays the same; only the pacing changes.
Riegel's formula scales a race time to other distances, assuming you slow slightly as distance grows. It's a guide, not a promise: it works best between similar distances, and assumes you've trained for the longer ones.
Riegel (1981) is a single power law fitted to world records. Daniels and Gilbert (1979) model oxygen cost of running speed and the share of VO₂max you can hold for a given time, giving a fitness score called VDOT. A second race of your own lets you fit your personal exponent instead of assuming 1.06. All three use the race from the calculator above.
k = ln(3:55:00 / 50:00) ÷ ln(42.195 / 10) = 1.075Within the normal range. Riegel’s 1.06 came from records across distances.A standard track has two 84.39 m straights and bends with a 36.50 m inner radius. Distance is measured 0.30 m outside the kerb in lane 1 and 0.20 m outside the line in other lanes, each 1.22 m wide. Every lap below is computed from that geometry at your pace.
A watch adds up straight lines between position fixes. Random error in each fix makes the zigzag longer than the real path; recording fixes further apart cuts the corners and makes it shorter. This simulates 5 laps of a 250 m city block at your pace, with real Gaussian position noise, 30 times per setting.
Exact lengths, the measuring rules behind them, and your pace applied to each.
Neighbouring calculators, with a typical result for each.