Dew Point Calculator
Calculate the dew point temperature based on current temperature and relative humidity. This tool helps meteorologists, HVAC professionals, and homeowners determine when condensation will form.
How to Use This Dew Point Calculator
- Enter the current air temperature
- Enter the relative humidity percentage
- Select your preferred temperature units
- Click “Calculate Dew Point”
- View results in your preferred unit (°C or °F)
Dew Point Formula
The calculator uses the Magnus-Tetens formula to determine dew point:
Td = (b × α(T,RH)) / (a – α(T,RH))
Where:
- α(T,RH) = (a × T)/(b + T) + ln(RH/100)
- Td = Dew point temperature (°C)
- T = Air temperature (°C)
- RH = Relative humidity (%)
- a = 17.27 (constant)
- b = 237.7 (constant)
Understanding Dew Point
The dew point is the temperature at which air becomes saturated with water vapor. When air cools to its dew point, condensation forms (dew, fog, or frost). Key facts:
- High dew point (>18°C/65°F): Humid, uncomfortable air
- Low dew point (<10°C/50°F): Dry, comfortable air
- Dew point = air temperature: 100% humidity (fog or rain)
Practical Applications
Weather Forecasting
Predict fog, frost, or precipitation when temperature approaches dew point.
HVAC Systems
Prevent condensation on cold surfaces by maintaining proper dew point.
Agriculture
Determine optimal conditions for crops and prevent frost damage.
Home Maintenance
Identify potential mold growth areas where surfaces reach dew point.
Dew Point Calculator: The Complete Guide to Measuring Moisture in Air
Introduction: What is Dew Point?
Dew point is a key weather and comfort measurement. It tells you when moisture will condense from the air. Understanding dew point helps with:
✔ Predicting fog and frost
✔ Controlling indoor humidity
✔ Preventing mold growth
✔ Improving industrial processes
A Dew Point Calculator makes these calculations easy. This guide explains everything about dew point. You’ll learn how to calculate it manually and use our free tool.
What is Dew Point?
Dew point is the temperature at which air becomes saturated with water vapor. When air cools to this point, water condenses into dew or frost.
Key facts about dew point:
- Measured in degrees (°F or °C)
- Higher dew point = more moisture in air
- Below freezing = frost point
- Affects comfort, health, and equipment
Dew Point vs. Humidity: What’s the Difference?
Many people confuse dew point with relative humidity (RH). Here’s how they differ:
| Factor | Dew Point | Relative Humidity |
|---|---|---|
| Measures | Actual moisture in air | % of moisture relative to max |
| Changes with Temperature? | No | Yes (changes as air warms/cools) |
| Comfort Indicator? | Better (shows true moisture) | Less accurate |
Example:
- 90°F day with 50% RH = Dew point 68°F (humid)
- 70°F day with 90% RH = Dew point 67°F (similar moisture, but feels muggier)
Why is Dew Point Important?
1. Weather Forecasting
- Predicts fog, frost, and storms
- High dew points = muggy, uncomfortable air
- Low dew points = dry conditions
2. Health & Comfort
- Above 65°F (18°C): Humid, sticky air
- 50-65°F (10-18°C): Comfortable
- Below 50°F (10°C): Dry, crisp air
3. Preventing Mold & Damage
- Dew point above 60°F indoors? Risk of mold growth
- Condensation on windows? Air is too humid
4. Industrial & Scientific Uses
- HVAC system design
- Food storage & drying processes
- Paint and coating applications
How to Calculate Dew Point (3 Methods)
Method 1: Simple Dew Point Formula
If you know temperature (°C) and relative humidity (RH%):
- Calculate saturation vapor pressure (es):
es = 6.11 × 10^(7.5 × T / (237.7 + T))
(T = temperature in °C)
- Find actual vapor pressure (e):
e = (RH% / 100) × es- Calculate dew point (Td):
Td = (237.7 × log10(e / 6.11)) / (7.5 - log10(e / 6.11))Example:
- Temperature = 25°C (77°F)
- RH = 60%
- Dew point ≈ 16.7°C (62°F)
Method 2: Dew Point Approximation (Fast Rule)
For a quick estimate:
- Subtract 10°F from air temperature if RH is ~50%
- Subtract 15°F if RH is ~70%
- Subtract 20°F if RH is ~90%
Example:
- 80°F with 70% RH → Dew point ≈ 65°F
Method 3: Use Our Free Dew Point Calculator
Our Dew Point Calculator does the math instantly. Just enter:
- Temperature (°F or °C)
- Relative Humidity (%)
It calculates:
✅ Dew point
✅ Frost point (if below freezing)
✅ Comfort level
[Try the Calculator Here]
Dew Point Chart for Quick Reference
| Dew Point (°F) | Perceived Humidity | Comfort Level |
|---|---|---|
| Below 50°F (10°C) | Very dry | Comfortable |
| 50-60°F (10-16°C) | Mild | Pleasant |
| 60-65°F (16-18°C) | Slightly humid | A bit sticky |
| 65-70°F (18-21°C) | Humid | Uncomfortable |
| Above 70°F (21°C) | Very humid | Oppressive |
How to Use Dew Point in Daily Life
1. Home Humidity Control
- Ideal indoor dew point: 50-55°F (10-13°C)
- Use a hygrometer to monitor
- Run a dehumidifier if dew point >60°F
2. Preventing Window Condensation
- If windows fog up: Indoor dew point is too high
- Solution: Improve ventilation or reduce humidity
3. Outdoor Activities
- Dew point >65°F? Expect muggy conditions
- Dew point <32°F? Risk of frost
4. Industrial & Storage Safety
- Electronics: Keep dew point below 60°F to prevent corrosion
- Food storage: Low dew point prevents spoilage
Common Questions About Dew Point
Q: Can dew point be higher than temperature?
A: No. If air reaches 100% RH, dew point = current temperature.
Q: What’s the highest possible dew point?
A: Rarely exceeds 85°F (30°C) – extreme humidity (e.g., tropical climates).
Q: Why does dew point matter in winter?
A: Low dew points mean dry air, increasing static electricity and dry skin.
Q: How is dew point measured?
A: With a hygrometer or calculated from temperature + humidity.
Free Dew Point Calculator Tool
Our interactive calculator makes it easy:
- Enter temperature (°F or °C)
- Input relative humidity (%)
- Get instant dew point results
Bonus Features:
✔ Frost point detection
✔ Comfort level indicator
✔ Tips to adjust humidity
[Try It Now]
Conclusion: Why Dew Point Matters
Dew point is the best way to measure true moisture in air. Unlike relative humidity, it doesn’t change with temperature.
Key Takeaways:
✅ High dew point = muggy air (above 65°F)
✅ Low dew point = dry air (below 50°F)
✅ Indoor dew point should be 50-55°F
✅ Use our calculator for instant results
Monitor dew point to improve comfort, prevent mold, and plan outdoor activities better!