Running Humidity Calculator
Calculate humidity-adjusted running pace using dew point. Understand how muggy conditions affect your performance with research-backed pace adjustments for races and training.
Adjust Your Pace for Humidity
Calculate humidity-adjusted paces using dew point
Enter your cool, dry weather target pace to see what pace to run in humid conditions for equivalent effort.
Weather Conditions
Why dew point? Dew point is the best predictor of humidity's effect on running. Unlike relative humidity, dew point tells you exactly how muggy the air feels regardless of temperature. Most weather apps show dew point—look for it!
Dew Point: 18.0°C — Slightly Humid
Noticeable humidity. Some cooling impairment.
Dry Weather Pace
5:30
min/km
Target Pace in Humidity
5:37
min/km
Humidity Impact
-2.0%
speed reduction
Base DP Slowdown
2.5%
Temp Gating Factor
100%
Relative Humidity
65%
Run Type
Long
Dew Point Quick Reference
| Dew Point | Condition | Slowdown |
|---|---|---|
| < 55°F (13°C) | Dry | 0% |
| 55-60°F (13-16°C) | Comfortable | ~1% |
| 60-65°F (16-18°C) | Slightly humid | ~2-3% |
| 65-70°F (18-21°C) | Sticky | ~4% |
| 70-75°F (21-24°C) | Very humid | ~6-7% |
| 75-80°F (24-27°C) | Oppressive | ~12-15% |
| ≥ 80°F (27°C) | Extreme | 18%+ |
How this works: High humidity impairs sweat evaporation, your body's primary cooling mechanism. This raises core temperature and heart rate, reducing sustainable pace at a given effort. Dew point directly measures moisture in the air and predicts these effects better than relative humidity. The temperature gating factor accounts for research showing humidity only significantly affects performance above ~18°C (65°F).
Note: These calculations are based on dew point performance tables from running literature and lab research on humidity and endurance. Individual responses vary based on fitness, hydration, clothing, and personal heat tolerance. For very high dew points, prioritize safety over pace goals.
About the Running Humidity Adjusted Pace Calculator
Learn more about the calculator and its creator
Jonas
I have been a runner for over 10 years and I built this calculator to help runners like you and me with training and racing.
The Science of Humidity and Running Performance
Humidity significantly impacts running performance by impairing your body's primary cooling mechanism: sweat evaporation. This calculator uses dew point—the best predictor of "mugginess"—to estimate pace adjustments for humid conditions.
Why Dew Point Is Better Than Relative Humidity
Relative humidity (RH) is misleading because it's temperature-dependent. A 70% RH at 15°C feels completely different from 70% RH at 30°C. Dew point measures the absolute amount of moisture in the air, telling you exactly how muggy conditions are regardless of temperature.
Key insight: When dew point is high, sweat cannot evaporate efficiently no matter how hard you try. Your skin stays wet, core temperature rises, and sustainable pace decreases.
The Magnus Formula (Dew Point Calculation)
When you enter temperature and relative humidity, we calculate dew point using the Magnus approximation:
es(T) = 6.112 × exp(17.62T / (243.12 + T))
Where T = temperature (°C). Actual vapor pressure: e = es(T) × RH / 100
DP = 243.12 × ln(e/6.112) / (17.62 - ln(e/6.112))
This gives dew point in °C, which we convert to °F for the slowdown lookup.
Key Research on Humidity and Running
Several key studies inform our model:
- Maughan et al.: Found that in warm environments, increasing relative humidity significantly reduced time to exhaustion in prolonged exercise.
- Jenkins et al.: Reported approximately 3.4% impairment in cycling time trial performance when humidity was elevated, independent of temperature.
- El Helou, Mantzios marathon analyses: Large datasets showing temperature is primary, but humidity and dew point modulate effects above ~18°C (65°F).
- Coaching guidelines (Runner's Connect, Trail Runner, Fleet Feet): Dew point-based pace tables consistently used for race day adjustments.
Temperature Gating: Why Humidity Only Matters When It's Warm
Research shows humidity has minimal effect on performance when temperatures are below ~18°C (65°F). At cooler temperatures, your body can dissipate heat through other mechanisms (convection, radiation), and sweat evaporation is less critical.
Temperature Gating Factor (F_T):
- T ≤ 13°C: F_T = 0 (humidity effect negligible)
- 13°C < T < 18°C: F_T ramps from 0 to 1
- T ≥ 18°C: F_T = 1.0 (full humidity effect applies)
Dew Point Slowdown Table
Based on dew point tables from Runner's Connect, Trail Runner, and Fleet Feet, which compile research and race data:
| Dew Point | Condition | Base Slowdown |
|---|---|---|
| < 55°F (13°C) | Dry | 0% |
| 55-60°F (13-16°C) | Comfortable | ~1% |
| 60-65°F (16-18°C) | Slightly Humid | ~2.5% |
| 65-70°F (18-21°C) | Humid / Sticky | ~4% |
| 70-75°F (21-24°C) | Very Humid | ~6.5% |
| 75-80°F (24-27°C) | Oppressive | ~13.5% |
| ≥ 80°F (27°C) | Extreme | 18%+ |
Workout Type Factors
Humidity effects compound over time and with continuous effort. Lab work and field data show that long, continuous efforts suffer more than short intervals with recovery periods.
| Workout Type | Factor | Rationale |
|---|---|---|
| Marathon / Long Race | 100% | Maximum cumulative humidity stress |
| Long Tempo (30-90 min) | 80% | Significant continuous effort |
| Easy / Recovery Run | 60% | Lower intensity, less heat production |
| Intervals | 40% | Recovery allows partial cooling |
Heat/Humidity Acclimation
Acclimation to heat and humidity significantly improves tolerance. Reviews and experiments show that acclimated athletes have improved sweating efficiency, lower core temperature at a given intensity, and better cardiovascular response.
| Acclimation Status | Factor | Effect |
|---|---|---|
| Not Acclimated | 1.2× | 20% more sensitivity to humidity |
| Partially Acclimated | 1.0× | Reference baseline |
| Well Acclimated | 0.8× | 20% less sensitivity to humidity |
Combined Slowdown Formula
Total humidity slowdown:
s_humid = s_dp × F_T × F_work × F_accl
Where:
- s_dp = base dew point slowdown (from table above)
- F_T = temperature gating factor (0 to 1)
- F_work = workout type factor (0.4 to 1.0)
- F_accl = acclimation factor (0.8 to 1.2)
Result is clamped between 0% and 20%.
Pace Mode vs Effort Mode Math
Slowdown is defined on speed, not pace, which creates the proper mathematical relationship:
Effort Mode (dry target → humid pace):
p_humid = p_dry / (1 - s_humid)
Example: 5:00/km dry, 5% slowdown → 5:16/km in humidity
Pace Mode (humid pace → dry equivalent):
p_dry = p_humid × (1 - s_humid)
Example: 5:16/km in humidity, 5% slowdown → 5:00/km equivalent dry
How This Differs from the Heat Calculator
- Heat Calculator: Uses heat index to model total temperature + humidity effect together
- Humidity Calculator: Uses dew point directly to isolate the extra penalty from muggy air
- Temperature gating: Explicitly turns off humidity effects at cool temperatures (< 18°C)
- Use cases: Heat calculator for overall conditions; humidity calculator to understand mugginess specifically
Example Calculation
Conditions: 25°C, 70% RH → Dew point ~19°C (66°F), Long tempo, partially acclimated
1. Dew point category: 65-70°F → s_dp = 4%
2. Temperature gating: 25°C > 18°C → F_T = 1.0
3. Workout factor: Long tempo → F_work = 0.8
4. Acclimation: Partial → F_accl = 1.0
5. Combined: 4% × 1.0 × 0.8 × 1.0 = 3.2% slowdown
6. Result: 5:00/km dry → 5:10/km in these humid conditions
Limitations and Caveats
- This is a heuristic model based on dew point tables and research, not individualized testing
- Individual variation is significant—some runners handle humidity better than others
- Hydration, clothing, and fitness all affect actual performance
- At very high dew points (≥ 75°F), health risks become more important than pace predictions
Important: For very high dew points, prioritize safety over pace goals. Signs of heat illness include dizziness, nausea, confusion, and cessation of sweating. Stop immediately if you experience any of these symptoms.
Related Tools & Guides
Dew Point Running Chart
Complete dew point slowdown tables
Dew Point vs Relative Humidity
Why dew point is better for runners
Humidity and Marathon Performance
Research on humidity effects in races
Running Heat Calculator
Combined temperature and humidity effects
Running Pace Calculator
Convert pace, speed, and finish time
Jack Daniels Calculator
VDOT and training paces
Altitude Running Calculator
Convert pace between elevations
Frequently Asked Questions
Dew point measures the absolute amount of moisture in the air, while relative humidity is temperature-dependent. A 70% RH at 15°C feels completely different from 70% RH at 30°C. Dew point tells you exactly how muggy it will feel regardless of temperature.
Below 55°F (13°C): Dry and comfortable. 55-60°F: Pleasant, minimal impact. 60-65°F: Slightly humid, 2-3% slowdown. 65-70°F: Sticky, 4% slowdown. Above 70°F: Oppressive conditions with significant performance impact.
High humidity impairs sweat evaporation, your body's primary cooling mechanism. When sweat can't evaporate, core temperature rises faster, heart rate increases, and sustainable pace decreases. Lab studies show 3-4% performance impairment from elevated humidity alone.
No. Research shows humidity has minimal performance impact when temperatures are below 18°C (65°F). Our calculator includes temperature gating that reduces the humidity effect at cooler temperatures.
Humidity effects accumulate over time. In short intervals with rest, your body can partially cool between efforts. During continuous long runs, heat and humidity stress compound progressively. That's why our calculator adjusts for workout type.
Effort Mode: Enter your cool, dry weather target pace and see what pace to run in humid conditions for equivalent effort. Pace Mode: Enter the pace you actually ran in humidity and see what it equals in ideal conditions.
Most weather apps display dew point. Check the detailed weather view on apps like Weather.com, AccuWeather, or your phone's built-in weather app. Look for 'Dew Point' alongside temperature and humidity.
Yes. Heat acclimation improves sweating efficiency and cardiovascular response, which helps in humid conditions too. Well-acclimated runners typically experience 20-30% less performance penalty in muggy weather.
When dew point exceeds 75°F (24°C), conditions become oppressive and health risks increase. Above 80°F (27°C) dew point, outdoor running is not recommended, especially for long efforts. Consider indoor alternatives or early morning running.
The model uses dew point slowdown tables from running literature (Runner's Connect, Fleet Feet) and lab research (Maughan, Jenkins). Individual responses vary based on fitness, hydration, and personal heat tolerance. Use as a guide for setting realistic pace expectations.
Why is dew point better than relative humidity for runners?
What dew point is comfortable for running?
How does humidity affect running performance?
Does humidity matter when it's cool outside?
Why do long runs suffer more from humidity?
What is the difference between Pace Mode and Effort Mode?
How do I find the dew point?
Does heat acclimation help with humidity tolerance?
When should I avoid running due to humidity?
How accurate is this calculator?
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