Estimate a heat-adjusted running pace
Use temperature, humidity and exposure to build a more realistic race pace estimate.
This is a planning estimate, not a measured WBGT value or a medical safety assessment. Acclimatisation, wind, cloud, clothing, hydration, course profile and individual response can change the outcome.
Plan a realistic pace for hot conditions
Heat can make a pace that feels controlled in cool weather become unsustainable. This calculator estimates a more realistic target using your normal-condition pace, race distance, air temperature, relative humidity and expected sun exposure.
The output includes an estimated slowdown percentage, adjusted pace, time added per kilometre and mile, and a projected finish time.
How to use the calculator
- Enter the pace you would normally target in mild conditions.
- Select the race distance.
- Enter the expected air temperature and relative humidity.
- Choose shaded, mixed or exposed conditions for solar load.
Why temperature alone is not enough
Humidity reduces the effectiveness of sweat evaporation, while direct sun increases environmental heat load. Wind, cloud cover and the amount of shade can also change how the same air temperature feels during a race.
Research across endurance events has found that combined measures such as wet-bulb globe temperature can explain performance effects better than air temperature alone. ToolCetra therefore uses temperature together with humidity, exposure and distance rather than applying one universal percentage.
How to use the estimate on race day
- Start from the adjusted pace rather than trying to bank time early.
- Use effort and heart-rate trends as additional checks.
- Expect exposed sections and late-race fatigue to feel harder.
- Review organiser guidance, aid stations and local heat alerts.
Important limitations
This is a planning estimate, not a measured WBGT reading and not medical advice. The model cannot fully account for heat acclimatisation, hydration, clothing, wind, cloud cover, fitness, medication, illness or individual heat tolerance.
Stop exercising and seek appropriate help if you develop concerning symptoms. Do not use a predicted finish time to override race-organiser instructions or health guidance.
Method context: weather parameters and endurance performance across 1,258 races.
Frequently asked questions
Is the adjusted pace guaranteed?
No. It is a sensible starting estimate. Individual responses to heat vary significantly.
Why does race distance affect the result?
Longer events create more time for heat strain and dehydration to accumulate, so the same conditions can have a larger practical effect.
Should I enter the forecast high temperature?
Use the expected temperature during your race, especially around the later stages, rather than the daily maximum if it occurs after you finish.
Can I use the result for training?
Yes, as a pacing guide. For workout intensity, also use perceived effort and consider the Training Pace Calculator.