What is Relative Humidity?

Relative humidity is a measure of how much water vapor is in the air compared to the maximum amount of water vapor the air could hold at that specific temperature. It is expressed as a percentage. When the humidity is 100%, the air is fully saturated, and water may begin to condense into dew or fog.

How to Calculate Humidity from Dew Point

The most common way to calculate humidity when you know the temperature and the dew point is by using the August-Roche-Magnus formula. This formula estimates the saturation vapor pressure and actual vapor pressure. The ratio between these two values gives us the relative humidity.

Understanding the Formula

1. First, we calculate the Saturation Vapor Pressure (Es) using the actual air temperature.
2. Next, we calculate the Actual Vapor Pressure (E) using the dew point temperature.
3. Finally, we divide E by Es and multiply by 100.

Mathematically, the pressure constant used is typically 17.625 and 243.04. The higher the temperature, the more moisture the air can hold, which is why relative humidity often drops during the day as temperatures rise even if the moisture content remains the same.

Why Use This Tool?

This Humidity Calculator with Steps is essential for HVAC professionals, meteorologists, and hobbyists. Unlike simple calculators, it provides the underlying mathematical steps so you can verify the physics behind the calculation. It supports both Celsius and Fahrenheit scales to ensure global usability.

Frequently Asked Questions

Q: Can humidity exceed 100%?
A: In natural outdoor environments, it rarely exceeds 100%. If it does, the air becomes supersaturated, usually leading to immediate precipitation or cloud formation.

Q: What is a comfortable humidity level?
A: Most people find a relative humidity between 30% and 50% to be the most comfortable for indoor living environments.