HumidCalc

＊Weather data supported＊

A versatile humidity calculation app for everyone from general users to engineers — also suitable for agricultural applications.

This app allows you to easily calculate indicators such as the Discomfort Index, WBGT (estimated heat stress index), Volumetric Absolute Humidity (an important indicator for influenza prevention), and Humidity Deficit (HD) used in agriculture, using weather data.

You can also calculate a wide range of air properties from dry-bulb temperature (normal air temperature) and wet-bulb temperature obtained from ventilated psychrometers such as the Assmann psychrometer.
Atmospheric pressure can be entered manually.

The app supports 11 indicators across 15 calculation items, and unit conversion between Celsius/Fahrenheit and SI/Imperial units can be performed instantly by switching the temperature unit setting.

■ High-Precision Calculation Engine

This app uses the Wexler–Hyland equations combined with numerical analysis, enabling highly accurate and stable calculations across a wide range of environmental conditions.

■ Calculable Indicators

* Dew Point Temperature

* Frost point tempreature

* Relative Humidity

* Humidity Ratio(Absolute Humidity)

* Mass-based absolute humidity

* High-resolution mass-based absolute humidity

* Volumetric absolute humidity

* Humidity Deficit (HD)

* Vapor Pressure Deficit (VPD)

* Enthalpy

* Specific Volume

* Equilibrium Vapor Pressure

* Partial Pressure

* Boiling Point of water

* WBGT (estimated value)

* Discomfort Index (DI)

Supplementary Notes on WBGT & Discomfort Index

Outdoor WBGT is defined as:

WBGT = 0.7 Tnw + 0.1 Td + 0.2 Tg

Since globe temperature (Tg) is not an input parameter, it is estimated from dry-bulb temperature (Td) using:

Tg = 1.45 Td − 27.162 (°F)

Td and Tg show a strong correlation (n = 17,376, R² = 0.919).

Natural wet-bulb temperature (Tnw) is obtained by converting the measured wet-bulb temperature from an Assmann psychrometer to natural conditions, assuming a wind speed of 0.5 m/s (1.64 ft/s) or less.

Details of this conversion algorithm are omitted.

The Discomfort Index (DI) is calculated as:

DI = 0.4 × (Td + Tw) + 15 (°F).

■ Weather Data & Sensors

By tapping the Weather Data button, you can obtain current atmospheric pressure, dry-bulb temperature, and wet-bulb temperature.

On devices equipped with a barometric pressure sensor, pressing the MEAS button allows direct pressure measurement.

Wet-bulb conditions can be set to Normal or Frozen (effective below freezing).

Corrected values can also be displayed for non-ventilated psychrometers such as the August psychrometer (ventilated types recommended for accuracy).

■App Ecosystem Integration

You can directly receive calculated dry-bulb and wet-bulb temperatures from the companion app “Calculator of Air”.
(Please note that calculations must be performed in Calculator of Air before data can be transferred.)

By combining HumidCalc with Calculator of Air, you can, for example, derive multiple air properties from known dry-bulb temperature and relative humidity values.

■Input Ranges

* Dry-bulb & wet-bulb temperature: −30°C to 50°C (−22°F to 122°F)

* Atmospheric pressure: 600 hPa to 2475 hPa (17.72 inHg to 73.09 inHg)

■Data Source

This app uses OpenWeatherMap data (CC BY-SA 4.0).

■Notes

When using an August psychrometer, calculations assume an air velocity at the sensing element of 0.5 m/s or less.
As a result, calculated values may differ from those listed in humidity tables included with commercial August psychrometers.

■Disclaimer

1. Please use values within reasonable temperature ranges (approximately 0°C to 40°C / 32°F to 104°F). Extremely unusual inputs may produce inaccurate results.

2. While every effort has been made to ensure high precision, minor errors may occur due to floating-point limitations.

3. The developer assumes no responsibility for any damages resulting from the use of this app.