Race Time Calculator Adjusted for Weather
Roughly what you'll run — adjusted for heat, wind and elevation
Distance and fitness
A recent race in good conditions sets your baseline — give a result or an average pace per km. Your pace drives the heat penalty: the slower you are, the bigger it gets.
Conditions
Course
We don't ask for wind direction — nobody knows it a month out. The estimate is always computed both ways (a headwind takes more than a tailwind gives back); a point-to-point course also gets a range under the wind line. Why, in the FAQ below.
Filled in from the chosen city — adjust if the start is much higher or lower. Matters on longer races: thin air slows a non-acclimatised runner.
Result
Kilometre splits
The usual race-time calculator scales your result in a vacuum: enter a recent time, get a prediction from the Riegel exponent. A real race in the heat, into a headwind or up a hill runs differently, and this calculator shows by how much: the plain prediction and the conditions-adjusted time sit side by side, with a breakdown underneath — how many minutes the heat cost you, how many the wind, how many the elevation.
The key difference is that the heat penalty depends on your speed. A slower runner loses four to five times more at 28 °C than a fast one; other calculators, when they account for temperature at all, give everyone the same correction. Weather for your date and start hour is pulled in automatically. The number is an estimate, not a promise of seconds.
FAQ
Why is my heat penalty larger than my friend's?
Because it scales with pace. Per Vihma (2009) and El Helou (2012), runners slow above 15 °C, and the slower the pace the more: roughly 0.6 seconds per kilometre per degree at a fast pace, up to 2.8 at a slow one. So a slower runner in the same conditions takes a much bigger hit.
Why doesn't it ask for wind direction?
Nobody knows it a month out, and even knowing it you can't turn it into head/tailwind without the course bearing. So the central estimate is always computed both ways — which is also the expected value when the direction is unknown. For a point-to-point course, a range from tailwind to headwind is shown under the wind line.
How much should I trust the number?
It is an order-of-magnitude estimate. The formulas come from research (heat from Vihma and El Helou, elevation from the Minetti 2002 polynomial, wind from aerodynamics and the Da Silva 2022 metabolic cost, altitude from a Daniels-style estimate), but humidity and rain are a mild heuristic. What happens on the day — how you feel, fuelling, how you pace it — the model can't see. More than two weeks out, the weather is also a past-years average rather than a forecast.
Which result do I put in the 'recent result' field?
Any honest race from the last week or two in comfortable weather on an easy course: 5K, 10K, a half. It sets your baseline via the Riegel formula, and the target race's conditions are layered on top. The closer the reference distance to your target, the better.