Power Calculators

☁️ Cloud Base Calculator

Estimate cloud base height above ground from surface temperature and dew point using the standard aviation temperature-dew-point spread method.

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Enter details

Enter surface air temperature.
Enter the dew point at the same location and approximately the same time.
Optional elevation of the observation point above mean sea level.

Fill in the details and click Calculate to see your results.


Also available in our Android app, with charts and full breakdown tables.

📘 About the Cloud Base

Cloud base is the height above the ground where the visible cloud begins.

A common aviation estimate uses the difference between surface temperature and dew point.

When temperature and dew point are close together, saturation is reached at a lower altitude.

When the temperature-dew point spread is larger, the estimated cloud base is higher.

✏️ Worked examples

Example 1 - 25°C and 15°C dew point

You enter
Air Temperature25
Dew Point15
Temperature UnitCelsius (°C)
Station Elevation0
Elevation UnitMeters
You get
Estimated Cloud Base AGL (ft)4,000
Estimated Cloud Base AGL (m)1,219
Estimated Cloud Base MSL (ft)4,000
Estimated Cloud Base MSL (m)1,219
Temperature-Dew Point Spread (°C)10
Temperature/Dew Point Relationship Valid (1 = Yes, 0 = No)1

The 10°C spread gives an estimated cloud base of approximately 4,000 feet AGL.

Try this example →

Example 2 - 18°C and 10°C dew point

You enter
Air Temperature18
Dew Point10
Temperature UnitCelsius (°C)
Station Elevation0
Elevation UnitMeters
You get
Estimated Cloud Base AGL (ft)3,200
Estimated Cloud Base AGL (m)975
Estimated Cloud Base MSL (ft)3,200
Estimated Cloud Base MSL (m)975
Temperature-Dew Point Spread (°C)8
Temperature/Dew Point Relationship Valid (1 = Yes, 0 = No)1

An 8°C spread gives an estimated cloud base of about 3,200 feet AGL.

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Example 3 - Near saturation

You enter
Air Temperature12
Dew Point12
Temperature UnitCelsius (°C)
Station Elevation100
Elevation UnitMeters
You get
Estimated Cloud Base AGL (ft)0
Estimated Cloud Base AGL (m)0
Estimated Cloud Base MSL (ft)328
Estimated Cloud Base MSL (m)100
Temperature-Dew Point Spread (°C)0
Temperature/Dew Point Relationship Valid (1 = Yes, 0 = No)1

When temperature and dew point are equal, the estimated cloud base approaches ground level, consistent with fog or very low cloud conditions.

Try this example →

🧭 How to use this calculator

What you enter

  • Air TemperatureEnter surface air temperature.
  • Dew PointEnter the dew point at the same location and approximately the same time.
  • Temperature Unit
  • Station ElevationOptional elevation of the observation point above mean sea level.
  • Elevation Unit

What you get

  • Estimated Cloud Base AGL (ft)
  • Estimated Cloud Base AGL (m)
  • Estimated Cloud Base MSL (ft)
  • Estimated Cloud Base MSL (m)
  • Temperature-Dew Point Spread (°C)
  • Temperature/Dew Point Relationship Valid (1 = Yes, 0 = No)

💡 Cloud base formula

  • Cloud base in feet AGL ≈ ((temperature - dew point) / 2.5) × 1,000.
  • A convenient mental approximation is about 400 feet per degree Celsius of spread.
  • The calculation estimates the lifting condensation level for a rising parcel under simplified conditions.

💡 AGL versus MSL

  • AGL means above ground level.
  • MSL means above mean sea level.
  • The temperature-dew point calculation estimates height above the observation surface.
  • Adding station elevation converts the estimated height to an approximate MSL altitude.

💡 Limitations

  • This is not a replacement for an observed ceilometer or official aviation weather report.
  • Frontal, orographic, inversion-capped and fog conditions may not follow this simple relationship.
  • Actual cloud base can differ substantially from the estimate.
  • Pilots should use official METAR, TAF and aviation weather information for flight decisions.

❓ Frequently asked questions

How is cloud base estimated?

A common aviation approximation estimates cloud base from the surface temperature minus dew point spread.

What is the cloud base formula?

Cloud base in feet AGL is approximately ((temperature in °C - dew point in °C) / 2.5) × 1,000.

What does AGL mean?

AGL means above ground level.

What does MSL mean?

MSL means mean sea level.

What happens when temperature equals dew point?

The estimated cloud base approaches the ground, indicating saturation and potentially fog or very low cloud.

Is this cloud base exact?

No. It is a simplified estimate and actual cloud bases depend on atmospheric structure and cloud formation processes.