The saying “some like it hot, some like it cold” definitely rings true when it comes to runners’ opinions on the best weather for running.
While some runners swear by the challenge of a hot summer run and others prefer the crispness of winter, most agree that the ideal temperature lies somewhere in between.
But what is the Goldilocks temperature for running—not too hot, not too cold, but just right?
Research varies on the exact answer, as the optimal running temperature can depend on factors such as experience level and pace. However, studies suggest that most runners perform best within a temperature range of 3.8°C to 9.9°C (38.9°F to 49.8°F).
In this guide, we’ll explore the science behind the best running weather and take a closer look at how heat, humidity, and other environmental factors can affect your performance.
What Is the Best Temperature for Running?
The best temperature for running is really only a piece of the puzzle. Other environmental factors, such as humidity and dew point, can significantly impact the “real feel” or heat index.
The heat index is a composite score that considers not only the air temperature but also the relative humidity, giving you a sense of how hot it actually feels.
Running in hot and humid conditions is even more taxing on the body than running in the heat, as the air’s higher moisture content makes it feel even hotter. In fact, the thermal strain of running in the heat increases exponentially—not linearly—with an increase in humidity.
For example, when the temperature is 88°F (31 °C) and the humidity is 40%, it will feel like 88°F.
However, when the temperature is 88° F with 70% humidity, it feels like 100° F (38° C). At the same temperature, a humidity level of 85% increases the heat index to 110° F (43° C).
When the humidity is 40% or less, it has a minimal effect on the heat index or how hot it actually feels while running in hot weather. However, once the humidity exceeds 40%, the heat index has a significant, exponential impact.
This mathematical relationship makes calculating the heat index by hand challenging, but there are numerous online calculators available, such as the one provided here.
One study1El Helou, N., Tafflet, M., Berthelot, G., Tolaini, J., Marc, A., Guillaume, M., Hausswirth, C., & Toussaint, J.-F. (2012). Impact of Environmental Parameters on Marathon Running Performance. PLoS ONE, 7(5), e37407. https://doi.org/10.1371/journal.pone.0037407 compared the results of six marathons based on four environmental factors: temperature, humidity, dew point, and the atmospheric pressure at sea level.
The results suggested that air temperature had the most significant effect on running performance and dropout rates of the four environmental factors considered.
Air temperature was correlated with running for both sexes and all performance levels, while humidity affected faster women and men of all levels.
The more the air temperature increased above the “optimal running temperature,” the slower the running speeds and the higher the withdrawal rates.
These optimal running temperatures are likely colder than many runners would anticipate, ranging from 3.8°C to 9.9°C (38.9°F to 49.8°F), depending on the performance level.
Interestingly, these two extremes were observed between the men’s and women’s elite runners, with male elites running fastest at the coldest end of the “ideal running temperature” range (3.8°C or 38.9°F), while the elite women runners were at the other extreme, at 9.9°C or 49.8°F.
The optimal temperature for running for average runners fell in the middle.
The best temperature for running—which was the temperature where runners ran the fastest—for each performance level was as follows:
| Performance Level | Ideal Running Temperature for Men (°F) | Ideal Running Temperature for Men (°C) | Ideal Running Temperature for Women (°F) | Ideal Running Temperature for Women (°C) |
| Elite Runners (top 1% of runners) | 38.9 | 3.81 | 49.8 | 9.91 |
| Top Quartile (top 25% of finishers) | 42.8 | 6.02 | 44.3 | 6.85 |
| Median | 43.2 | 6.24 | 44.15 | 6.75 |
| Third Quartile | 45.4 | 7.42 | 45.2 | 7.35 |
These results suggest that the optimal temperature for running for most individuals is around 5.9°C (42.6°F) for men and 7.7°C (45.9°F) for women.
These ideal running temperatures were determined by taking the average ideal temperature for the top quartile, median, and third quartile of runners for each sex.
A separate study2Knechtle, B., Di Gangi, S., Rüst, C. A., Villiger, E., Rosemann, T., & Nikolaidis, P. T. (2019). The role of weather conditions on running performance in the Boston Marathon from 1972 to 2018. PLOS ONE, 14(3), e0212797. https://doi.org/10.1371/journal.pone.0212797 which examined the relationship between Boston Marathon race results and the weather on race day found that the optimal temperature for running performance is between 44° F and 59° F (7–15° C), though the best results occur at wet bulb temperatures below 7.8 °C (46 °F).
The researchers noted a relatively linear relationship of slower average marathon runner finish times for each additional 1 °C increase in temperature.
What Happens To Runners In The Heat?
Every runner who has ventured out for a run on a hot and humid day knows that running in an environment that resembles a tropical rainforest is not easy.
Running increases your core body temperature, but the body wants to maintain your temperature within a narrow range to protect your brain and other tissues from overheating.
This is where the sweating response comes into play. The evaporative cooling process can help lower your core temperature by releasing heat energy through the evaporation of sweat droplets on the surface of your skin.
On a hot, dry day, sweating can be a fairly effective means of reducing your body temperature, yet when it’s humid, the moisture content in the air prevents sweat from evaporating readily.3Che Muhamed, A. M., Atkins, K., Stannard, S. R., Mündel, T., & Thompson, M. W. (2016). The effects of a systematic increase in relative humidity on thermoregulatory and circulatory responses during prolonged running exercise in the heat. Temperature, 3(3), 455–464. https://doi.org/10.1080/23328940.2016.1182669
Consequently, most of the heat energy stays trapped in your body without the ability to get released. This causes heat to build up, increasing the risk of heat-related illnesses such as heat exhaustion and heat stroke.
From a practical standpoint, running in the heat or humidity feels harder because your heart rate increases compared to running at optimal temperatures.
Thermal strain—being too hot or having an elevated body temperature—is stressful for the body, which in and of itself can raise your heart rate.
Still, the primary reasons that your heart rate is higher running in the heat are that skin blood flow increases and plasma volume drops.
In addition to sweating, one of the natural thermoregulatory mechanisms your body has to maintain temperature homeostasis is increasing blood flow to the skin.
Pulling blood away from the core towards the skin’s surface helps cool the blood, effectively helping release excess heat.
When you are running in the heat, your muscles already demand a ton of oxygen and nutrients, so cardiac output is high.
Note that cardiac output refers to the total amount of blood your heart is circulating per minute and is the product of your heart rate in beats per minute multiplied by the stroke volume (the amount of blood ejected from the heart into circulation per beat).
When any tissue, such as your muscles, needs more oxygen and nutrients, the heart beats faster and/or contracts more forcefully to circulate a greater volume of blood to the tissues.
This is why your heart rate is much faster when you run than when you sit at your desk; your muscles demand more blood.
In terms of running in the heat and humidity, when the thermoregulatory mechanisms kick in and the body starts shuttling a lot of blood toward the skin for cooling, the cardiac output has to increase even further than it had to beyond satisfying the oxygen and nutritional demands of the muscles.
As a result, your heart beats even faster.
Furthermore, unless you’re so on top of your hydration needs while running in the heat that you remain adequately hydrated, your blood plasma volume will decrease due to water lost through sweat.
The more dehydrated you become, the smaller the amount of blood you’ll have in circulation. This means that your stroke volume will decrease.
Because stroke volume is the other component of cardiac output, any decrease in stroke volume must be compensated for by further increasing heart rate.
Most runners will experience a heart rate increase of about 10-20 beats per minute when running at 90°F (32 °C) compared to running at 75°F (23 °C).
Similarly, your breathing rate will increase because the lungs need more oxygen to fuel the overworking heart and muscles.
As can be seen, running in the heat can substantially elevate your heart rate and respiratory rate, making it feel much harder to run on a hot day than at the ideal running temperature. This, in turn, can impact your training or marathon performance if you are participating in a race.
How Much Slower Do You Run In the Heat?
The extent to which the temperature affects your running performance seems to be influenced by your pace.
The research indicates that distance runners who average a 5:45 min/mile pace or faster slow down about 1 second per mile for each 1° C (1.8° F) increase in temperature above 15° C (59° F).4Vihma, T. (2009). Effects of weather on the performance of marathon runners. International Journal of Biometeorology, 54(3), 297–306. https://doi.org/10.1007/s00484-009-0280-x
In contrast, runners who average 7:25-10:00 min/mile pace slow down 4-4.5 seconds per mile with this same temperature increase.
Even though we’d expect less of a time consequence for faster runners having a quicker pace, the relative effect of temperature seems less impactful for elite runners, perhaps due to the thermoregulatory benefits of having lower body fat.
So, what should you do when it’s hotter than that sweet spot running weather of 44° F and 59° F (7–15° C)? Drink water and electrolytes to stay hydrated. Run in the shade, preferably in the early morning or evening, and give yourself grace – it’s normal to slow down.
If there is a heat wave and the running conditions are unbearable, consider training indoors on a treadmill, where you can control the air temperature.
To ensure you stay as well-hydrated as possible, check out our hydration guides for runners:
