Psychrometer °F3.7 - App Store

Psychrometer °F is a psychrometric calculator for evaluating thermal comfort and moist-air conditions using U.S. customary units.
Adjust temperature and humidity easily with the on-screen dials. Temperatures are color-coded for quick reference, and a “Good” indicator appears when conditions are between 68-82°F and 30-60% relative humidity.
Choose from the following input combinations:
. Dry-bulb temperature and relative humidity
. Dry-bulb temperature and dew-point or frost-point temperature
. Dry-bulb temperature and wet-bulb temperature
The app displays or calculates:
. Dry-Bulb Temperature (°F)
. Wet-Bulb Temperature (°F)
. Dew Point / Frost Point (°F)
. Relative Humidity (%RH)
. Humidity Ratio / Mixing Ratio (gr/lb)
. Absolute Humidity (gr/ft³)
. Enthalpy (Btu/lb)
. Specific Volume (ft³/lb)
. Atmospheric Pressure (inHg)
. Vapor Pressure (inHg)
. Saturation Vapor Pressure (inHg)
Comfort Indices:
. Heat Index based on the U.S. National Weather Service method
. Simplified indoor WBGT based on dry- and wet-bulb temperatures
. Discomfort Index (DI)
The app also displays risk levels and easy-to-understand indicators for each selected index.
Atmospheric Pressure:
Choose from standard atmospheric pressure, the device’s built-in barometer on supported devices, or manual entry. Selecting the barometer may require Motion & Fitness access because iOS manages pressure-sensor permission through this setting.
Outdoor Conditions:
Tap the Outdoor Air button to retrieve the current temperature, relative humidity, and weather conditions for your location from Apple Weather. Location access is requested only when this feature is used.
This feature retrieves weather information; it does not directly measure the air conditions around your device.
Psychrometer Types:
. Assmann - Aspirated psychrometer with forced ventilation; provides the highest measurement accuracy.
. Wall-Mounted - August psychrometer using natural airflow; simple and convenient, but less accurate.
. Sling - Swung by hand to move air across the thermometers; portable and suitable for outdoor use.
Assmann is the default setting. Tapping Reset or Outdoor Air returns the app to Assmann mode. Wall-Mounted and Sling modes use wet-bulb input.
Psychrometric Process Reference:
You can also explore psychrometric processes without using a psychrometric chart.
. In dew-point input mode (°F DP), keep the dew point fixed and adjust the upper dial to observe heating and cooling changes.
. In wet-bulb input mode (°F WB), keep the wet-bulb temperature fixed and adjust the upper dial to observe humidification and dehumidification changes.
. To examine steam humidification, use relative-humidity input mode (%) and adjust the lower dial.
Calculation Methods:
The Sonntag equations are used for saturation vapor pressure. Vapor-pressure calculations use the Sprung, August, or Ferrel psychrometric relationships according to the selected psychrometer type. Relative humidity is calculated according to WMO conventions.
The input range is intentionally wide, but extreme combinations may increase numerical error or fall outside the practical range of the formulas. Rounding and internal unit conversions may also cause the least significant digits to change when switching input modes.
Results are provided for reference only. Although care is taken to ensure accuracy, results are not guaranteed. The developer is not responsible for any damage, loss, or disadvantage resulting from use of this app.
This app contains ads. A one-time in-app purchase removes the banner ad and the full-screen ad shown at launch.

Version History Added a one-time purchase option to remove ads.
Outdoor weather data is now provided by Apple Weather.
Improved Heat Index and WBGT displays.
Refined the Settings screen and English wording.
Improved permission handling, layout, and overall stability. 3.7 Aug 11 Added +/- buttons to the keyboard.
Display atmospheric pressure on the main screen. (Configure in Settings. Standard atmospheric pressure is sufficient for normal use.)
Enthalpy calculation now conforms to ASHRAE definition.
UI improvements. 3.6 May 11 Improved text readability.
Added a link to PsychrometerPro. 3.5 12/14/2025 Support for access to barometric pressure sensors, improved input dialing. 3.4 12/04/2024 Fixed a bug in which atmospheric pressure was not set upon initial installation.
Improved accuracy of absolute humidity. 3.3 05/27/2022 Added psychrometer type.
If you use a psychrometer, please choose from 3 types.
(When not using, please use it as it is as a Assmann.)
Asssmann ... Aspirator psychrometer. It is a forced ventilation type.
Simple ... August psychrometer.Old type without forced ventilation.Wall-mounted.
Sling ... Sling Psychrometer.Type that swings around by hand.
(If you press the reset button or the outside air button, it will return to the ventilation type. With the exception of the ventilation type, only wet bulb input is possible.)

Changed the dew point(°CDP) temperature display below freezing to the frost point(°CFP) temperature display.

Dark Mode support.Comfort range update.Other minor bug fixes. 3.2.5 07/08/2020 Bug fix of dew point temperature input below freezing point.
Improve back calculation accuracy of wet-bulb temperature.
Other display bug fixes. 3.2.1 01/27/2020 iPhoneX compatible
Other adjustments 3.2 08/14/2018 Display comfort in color.Add reset button. The value can be set.
Fixed minor bugs, such as when not recalculated by dialing. 3.1 06/16/2017 Equipped with input Dial. The value input became smooth and intuitive.
Added input mode. Added relative humidity input mode and dew point temperature input mode.input mode.
As usual, you can also calculate in wet bulb input mode.
Added open air input. You can automatically enter outside temperature and humidity from the weather information.(Please allow use of location information.)
Add absolute humidity conversion. Displays the weight absolute humidity and volume absolute humidity by switching.
Addition of saturated vapor pressure indication. The calculation formula uses exact SONNTAG expression.
In addition, we have added some minor improvements.Unified into US customary units.
higher versions like iOS 10 3.0 03/29/2017 iOS9 support 2.8 01/14/2016 Temperature–humidity index (Discomfort index) added 2.7 06/10/2015 Temperature–humidity index (Discomfort index) added 2.6 05/05/2015 Add Information view
Adjustment etc 2.5 01/10/2015 Supports for the barometric pressure sensor. iPhone6,iPhone 6 Plus 2.4 11/04/2014 iOS 7 Version
change to custom keypad 2.2 02/04/2014 Bug fixes dew point temperature is not reset to re-Conversion.
The change in the pressure unit hPa.
Changing the UI. 2.0 08/23/2013 minor bug fixes 1.1 07/11/2013 1.0 05/28/2013