Example Data Table
| Air Temp |
Dew Point |
Pressure |
Elevation |
Simple Height |
Bolton Height |
Hypsometric Height |
| 30 °C |
20 °C |
1010 hPa |
150 m |
1250 m |
1258.66 m |
1265.26 m |
| 24 °C |
18 °C |
1008 hPa |
25 m |
750 m |
755.26 m |
759.15 m |
| 12 °C |
10 °C |
990 hPa |
500 m |
250 m |
250.31 m |
251.59 m |
Formula Used
Simple spread estimate: LCL height = 125 × (T - Td). Height is in meters. T and Td are in Celsius.
Bolton LCL temperature: TLCL = 1 / [1 / (TdK - 56) + ln(TK / TdK) / 800] + 56.
Bolton height: height = (TK - TLCL) / dry lapse rate. The result is converted from kilometers to meters.
LCL pressure: PLCL = P × (TLCL / TK) ^ (1 / kappa). Kappa is about 0.2854.
Hypsometric height: height = Rd × mean temperature / g × ln(P / PLCL).
How to Use This Calculator
- Enter the observed air temperature.
- Enter dew point, or leave it blank and enter humidity.
- Add surface pressure for the pressure based method.
- Enter station elevation to get the sea level cloud base.
- Choose the method you want as the main result.
- Press calculate, or download the result as CSV or PDF.
Understanding the Lifted Condensation Level
The lifted condensation level, or LCL, is the height where a rising air parcel first becomes saturated. It is often used as a practical estimate of cloud base. A low LCL means clouds may form near the ground. A high LCL means the air must rise farther before visible cloud droplets appear.
Why This Estimate Matters
Pilots, forecasters, farmers, hikers, and storm spotters use LCL height often. It helps describe low cloud risk, fog potential, and thunderstorm bases. It also gives a quick view of moisture depth near the surface. Warm dry air usually creates a higher LCL. Cool moist air usually creates a lower LCL.
Main Inputs
This calculator uses air temperature and moisture data. You may enter dew point directly. You may also enter relative humidity, and the tool will estimate dew point. Surface pressure improves the pressure based method. Station elevation lets the page show both above ground level and above mean sea level heights.
Method Details
The simple spread method multiplies the temperature spread by about 125 meters. It is fast and works well for rough field checks. The Bolton method first estimates LCL temperature. Then it converts the parcel cooling amount into height. The pressure method uses dry adiabatic pressure change and the hypsometric equation. That gives a more detailed estimate when pressure is known.
Reading the Results
The main result is the selected method height. It is shown in meters and feet. The comparison values show how each method differs. Small differences are normal. Weather stations, surface heating, terrain, and mixing can change real cloud base height. Treat the output as an estimate, not a direct observation.
Good Practice
Use recent temperature and dew point readings. Choose a nearby pressure value when possible. Enter local station elevation if you need cloud base above sea level. Repeat the calculation when weather changes. Rising humidity lowers LCL height. Falling humidity raises it. Strong afternoon heating can also lift the cloud base quickly.
Limits to Remember
The LCL does not prove that clouds exist. Air may stop rising below that level. Dry layers can evaporate droplets. Local terrain can force extra lift. Use observations with the calculated value during changing weather today.
FAQs
What is the lifted condensation level?
It is the height where a lifted air parcel cools enough to become saturated. It often gives a useful estimate of cloud base above ground.
Is LCL the same as cloud base?
Not always. LCL is a calculated parcel level. Actual cloud base can differ because of mixing, terrain, vertical motion, and dry air layers.
Which method should I choose?
Use the Bolton method for a balanced estimate. Use the simple method for quick checks. Use the hypsometric method when reliable pressure data is available.
Can I use relative humidity instead of dew point?
Yes. Leave dew point blank, then enter relative humidity. The calculator estimates dew point with the Magnus equation before calculating LCL height.
Why is pressure included?
Pressure helps estimate LCL pressure and height through the hypsometric method. It is useful when comparing stations at different elevations.
What does AGL mean?
AGL means above ground level. It shows cloud base height above the local station or surface, not above sea level.
What does AMSL mean?
AMSL means above mean sea level. The calculator adds station elevation to the LCL height above ground.
Why do the methods give different results?
Each method uses different assumptions. The simple method uses only temperature spread. The other methods use LCL temperature, pressure, or lapse rate.