Calculadora de Umidade Relativa
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
UR = (e / e_sat) × 100; e ≈ e_sat(Tu) − 0,799·(Ts − Tu)
About this calculator
The Relative Humidity Calculator estimates relative humidity using dry-bulb and wet-bulb temperatures. Relative humidity (RH) is the ratio of actual vapor pressure to saturation vapor pressure, expressed as a percentage. The calculator uses a simplified psychrometric formula: RH = (e / e_sat) × 100, where e ≈ e_sat(Tw) − 0.799·(Td − Tw), with Td being dry-bulb temperature and Tw wet-bulb temperature.
To use the tool, enter the dry-bulb and wet-bulb temperatures in degrees Celsius. The calculator returns the approximate relative humidity. This calculation is useful in meteorology, agriculture, and HVAC, helping to understand thermal comfort, predict dew formation, and assess conditions for drying or material storage.
The formula assumes standard atmospheric pressure (1013.25 hPa) and does not account for altitude or local barometric pressure, which may introduce errors at high elevations. Additionally, the simplified equation is valid for temperatures above 0°C and below 100°C. For greater accuracy, use aspirated psychrometers or complete psychrometric tables.
Frequently asked questions
What is relative humidity?
Relative humidity is the amount of water vapor present in the air relative to the maximum amount the air can hold at the same temperature, expressed as a percentage.
Why is the wet-bulb temperature lower than the dry-bulb temperature?
The wet-bulb temperature is lower because evaporation of water from the wet bulb cools the thermometer, and the difference between the two temperatures indicates the dryness of the air.
Does this calculator work at high altitudes?
Not accurately, because the formula assumes sea-level atmospheric pressure. At high altitudes, lower pressure changes saturation values.
Can I use this calculator for temperatures below zero?
The simplified formula is valid for temperatures above 0°C. Below that, the presence of ice alters saturation pressure.
What is the difference between relative humidity and dew point?
Relative humidity is the percentage of saturation; dew point is the temperature at which air becomes saturated. They are related: the higher the RH, the closer the dew point is to the current temperature.