The short answer
The ideal marathon temperature for most runners is about 4–10 °C (39–50 °F) of air temperature, according to a study of 1.8 million finishes at six big-city marathons. Elite racing peaks a little warmer, at a WBGT of 7.5–15 °C (46–59 °F). Above the ideal, every degree slows you, and slower runners lose most.
Key takeaways
- Mass-marathon finishers ran fastest at 3.8–9.9 °C (39–50 °F) of air temperature.
- Elite performance falls 0.3–0.4% for every degree of WBGT outside 7.5–15 °C (46–59 °F).
- Slower runners lose more in the heat and run later into the warm part of the day.
- In our data, London met the elite window most often; Comrades never did.
On this page
Words this guide uses
- WBGT (wet bulb globe temperature)
- A heat-stress index that combines humidity, sunshine, wind and air temperature, used by race medical teams.
- Optimal temperature
- The air temperature at which a group of runners averaged its fastest speed in a study.
- ERA5
- A global hourly reanalysis of past weather from the Copernicus Climate Change Service, run by ECMWF.
- Pace-timed forecast
- The weather for each stretch of your route at the time you'll run it.
What is the ideal marathon temperature?
The ideal marathon temperature for most runners is cool: about 4–10 °C (39–50 °F) of air temperature. That's the range in which finishers at six of the world's biggest marathons ran their fastest average speeds.
Elite runners peak a little warmer, but everyone slows once it gets hot. The bigger picture is in our hub on running in heat and humidity. Here we look at what the studies found, and how often four great races actually got ideal weather.
The answer depends on how fast you are and when you'll finish. A 3-hour runner and a 5-hour runner in the same race meet different weather.
What does the research show?
Five large studies agree that warm air slows most runners. They differ on the exact numbers because they measured different runners and different weather.
| Study | Runners and races | Ideal conditions, °C (°F) | What warmer weather did |
|---|---|---|---|
| El Helou et al., 2012 | 1,791,972 finishes, Paris, London, Berlin, Boston, Chicago, New York, 2001–2010 | Air 3.8–9.9 (39–50), by performance level | Speed fell, more runners dropped out |
| Mantzios et al., 2022 | 7,867 top athletes, 1,258 endurance races, 42 countries | WBGT 7.5–15 (46–59), air 10–17.5 (50–64) | 0.3–0.4% slower per degree of WBGT outside the window |
| Ely et al., 2007 | Seven North American marathons, up to 36 years each | Fastest in the coolest band, WBGT 5.1–10 (41–50) | Top men 1.7% off the course record, rising to 4.5% at 20.1–25 (68–77) |
| Vihma, 2010 | Stockholm Marathon, Sweden, 1980–2008 | Not given as a range | Air temperature was the weather factor most linked to slower times |
| Knechtle et al., 2021 | 869,474 Berlin Marathon finishes, 1974–2019 | Highs below 15 (59) for runners 35 and over | Older age groups slowed on warmer days |
El Helou's team found air temperature mattered more than any other weather factor in their data. Mantzios's team found WBGT, which adds humidity and sun, predicted performance better than air alone.
How much does a warm race slow you?
A few per cent for fast runners, and more for everyone else. On a 4-hour marathon, every 1% is 2 minutes 24 seconds.
Take Mantzios's figure of 0.3–0.4% per degree. A race day 5 °C (9 °F) of WBGT above the ideal window would cost a top performance 1.5–2%. On a 4-hour time, that's 3 minutes 36 seconds to 4 minutes 48 seconds.
Ely's team found the 25th, 50th, 100th and 300th finishers slowed more than the winners as WBGT rose. Vihma saw the same at Stockholm, for finishing times up to 4.7 hours. Our guide to heat-adjusted pace calculators shows how to turn this into a race pace.
How often do big marathons get ideal weather?
Less often than you'd hope. We modelled every race day from 2015 to 2024 at four races, for a runner finishing in 4 hours (11 hours at Comrades). This is reanalysis, not a thermometer at the start line.
| Race | Race days | Start air, °C (°F) | Warmest air met, °C (°F) | Days in elite WBGT window |
|---|---|---|---|---|
| London Marathon, UK | 9 | 5.8–18.9 (42–66) | 9.2–21.6 (49–71) | 6 |
| Boston Marathon, USA | 9 | 3.2–21.1 (38–70) | 8.0–22.9 (46–73) | 4 |
| Berlin Marathon, Germany | 9 | 8.2–16.5 (47–62) | 13.4–23.4 (56–74) | 2 |
| Comrades Marathon, South Africa | 8 | 4.9–17.3 (41–63) | 20.9–26.5 (70–80) | 0 |
There was no race in 2020. Boston 2021 ran on 11 October, and London on 3 October 2021 and 2 October 2022. Comrades skipped 2020 and 2021, and ran on 28 August in 2022.
Cool isn't always ideal. Two of Boston's four "ideal" days, 2015 and 2018, brought cold rain. In 2018 a 4-hour runner would have felt about −3 °C (27 °F) when wet. Our marathon weather history has every year.
Why does your finish time change the ideal?
Because a slower runner is out longer and later, when the sun is higher. The same race can be ideal at the front and hot at the back.
At the Berlin Marathon on 26 September 2021, a 3-hour runner peaked at a WBGT of 21.6 °C (70.9 °F), Moderate. A 5-hour runner reached 22.9 °C (73.2 °F), High, and a hottest feels like of 29.1 °C (84 °F). At Boston on 15 April 2024, the hottest feels like rose from 26.6 °C (80 °F) for a 3-hour runner to 28.0 °C (82 °F) at 5 hours.
So if you're a mid-pack runner, look at the weather for your finishing hours, not the start.
What should you do if race day is warmer than ideal?
Lower your goal before the start, not at halfway. Then run by effort and drink to thirst.
- Adjust your pace early. A few per cent off from the first kilometre costs less than a blow-up later.
- Check the heat for your finish time. That's when it's warmest.
- Follow the flags. Our guide to marathon heat flags explains each colour.
Official race flags and medical advice override this article. It isn't medical advice.
Questions runners ask
Is 15 °C (59 °F) too warm for a marathon?
For an elite runner, no: Mantzios and colleagues (2022) found peak performance most likely at 10–17.5 °C (50–64 °F) of air temperature. For a mass-participation runner, it's a little above the 3.8–9.9 °C (39–50 °F) optimum El Helou and colleagues found. Expect a small slowdown, more if the sun is out and you'll finish after midday.
Is cold weather bad for marathon times?
Only well below the ideal. El Helou and colleagues (2012) found that large drops in air temperature below the optimum also slowed runners. Cold rain is the bigger risk: the ACSM's 1996 position stand warns that slow runners can become hypothermic over long distances in wet, windy weather. Our reanalysis of the 2018 Boston Marathon shows exactly that kind of day.
Does humidity change the ideal marathon temperature?
It depends which study you read. El Helou and colleagues (2012) found humidity and dew point had no significant effect once air temperature was known. Mantzios and colleagues (2022) found WBGT, which leans heavily on humidity and sun, predicted performance better than air temperature alone. On a hot, sunny race day, humidity clearly matters.
Why did the fastest Berlin runners do well on warmer days?
Knechtle and colleagues (2021) studied 869,474 Berlin Marathon finishes from 1974 to 2019. The very fastest times came on days with daily highs of 15–30 °C (59–86 °F). A likely reason is that elite runners finish before the afternoon high, but the study didn't test that. Runners aged 35 and over were slowed by highs above 15 °C (59 °F).
What is the ideal marathon temperature in Fahrenheit?
About 39–50 °F of air temperature for most finishers, from El Helou and colleagues' study of six big-city marathons (3.8–9.9 °C). Elite performance peaks at roughly 50–64 °F of air, or a WBGT of 46–59 °F, according to Mantzios and colleagues (2022). US forecasts give air temperature, so the first range is the one to compare with.
Your race, at your pace.
Pick Comrades, Berlin, London or Boston, set your finish time, and see the heat stress, feels like and dew point you’d have met at every landmark, on every race day from 2015 to 2024.
Sources and method
- PLOS ONE (2012). Impact of environmental parameters on marathon running performance (El Helou et al.)
- Medicine & Science in Sports & Exercise (2022). Effects of weather parameters on endurance running performance: discipline-specific analysis of 1258 races (Mantzios et al.)
- Medicine & Science in Sports & Exercise (2007). Impact of weather on marathon-running performance (Ely, Cheuvront, Roberts and Montain)
- International Journal of Biometeorology (2010). Effects of weather on the performance of marathon runners (Vihma)
- Frontiers in Physiology (2021). Trends in weather conditions and performance by age groups over the history of the Berlin Marathon (Knechtle et al.)
- American College of Sports Medicine (Medicine & Science in Sports & Exercise) (1996). ACSM position stand: heat and cold illnesses during distance running
- Copernicus Climate Change Service (ECMWF) (2026). ERA5 hourly data on single levels from 1940 to present
Study figures are quoted from the papers listed. The race-day table is RunFast's own: ERA5 hourly reanalysis (Copernicus Climate Change Service) along each course, timed to a runner finishing in 4 hours at Berlin, London and Boston and in 11 hours at Comrades. "Start air" is the air temperature at the start; "warmest air" is the highest the runner met; peak WBGT uses the Liljegren et al. (2008) model. A race day counts as "in the elite window" when the runner's peak WBGT stayed within 7.5–15 °C (Mantzios et al., 2022). Race days run from 2015 to 2024 with gaps: no 2020 races; Boston 2021 ran on 11 October, London 2021 on 3 October and 2022 on 2 October; Comrades had no race in 2020 or 2021, and 2022 ran on 28 August. The time-cost example applies Mantzios's 0.3–0.4% per degree to a 4-hour marathon. °F values are our conversions.
Wes Thomson
Wes Thomson builds RunFast, which times the heat, humidity and dew point to a runner's own pace along the route, and its sister Windline, live wind forecasts for cyclists. Both run on the same forecast engine. He writes these guides with one focus: what the weather will do to your run, kilometre by kilometre, and how to plan around it.