GrainPoint Psychrometric Calc
Dew point & grains calculator
Only for iPhone
$4.99 · Designed for iPhone. Not verified for macOS.
iPhone
Two readings, one answer: open the building up, or keep it closed and run the dehumidifier. Decided on grains, not relative humidity. Offline, no account.
It is 7am, the building is wet, and the only question is whether to open the windows. GrainPoint answers that one.
Type the inside reading and the outside reading. GrainPoint compares them on GRAINS — the actual weight of water each holds — and tells you whether ventilating would dry the place out or make the job longer.
THE MISTAKE IT EXISTS TO PREVENT
Outside at 85°F and 50% has a lower relative humidity than inside at 75°F and 60%. It feels drier. It is not drier: it holds about twelve more grains per pound. Open the windows on that and you have just pumped water into a building you are trying to dry.
GrainPoint names that case out loud when it happens, because every instinct says the opposite.
It also refuses to decide when the two readings are within a few grains of each other. A field hygrometer is commonly ±3% RH, and pretending a two-grain difference is a decision would be false precision.
READ ACROSS, BOTH STATES AT ONCE
Dry bulb, wet bulb, dew point, dew point depression, relative humidity, humidity ratio, enthalpy, specific volume and vapour pressure — for inside and outside side by side, which is how you actually use them.
Everything comes from the ASHRAE Fundamentals formulation, the same correlations the printed psychrometric chart is a plot of, computed directly rather than interpolated off a digitised chart. Separate saturation correlations over ice and over water, so a February job is right too.
CORRECTED FOR THE JOB
Humidity ratio is water per pound of DRY air, and thin air weighs less. At the same temperature and humidity, a job a mile up carries more grains than one at sea level. Set the altitude and every number accounts for it — barometric pressure, not an assumption.
DRYING TARGETS
Four published chamber targets in grains, from an aggressive first-day differential to an occupied-comfort band, with a line on each saying what it is for. Set one and the app tells you when the chamber has reached it.
Fahrenheit and grains per pound, or Celsius and grams per kilogram. Switch any time.
WHAT IT IS NOT
It describes the air, not the material. It does not read moisture content in wood or drywall, size a dehumidifier, assess mould, or replace metering the material itself. The ventilate-or-dehumidify verdict compares two readings you took — it does not know what the weather will do next. The app says all of this on its own Reference screen.
Works offline. No account.
Ratings & Reviews
- This app hasn’t received enough ratings or reviews to display an overview.
• Metric enthalpy now uses the standard SI reference point.
The developer, Yaniv van der Stigchel, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Collected
The developer does not collect any data from this app.
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Yaniv van der Stigchel
- Size
- 5.4 MB
- Category
- Utilities
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
English and 4 more
- English, Dutch, German, Italian, Portuguese
- Age Rating
4+
- 4+
- Copyright
- © 2026 Yaniv Vanderstigchel
