Psychro Calc Pro for iPhone, on the App Store. Enter any two parameters — dry-bulb temperature, wet-bulb temperature, relative humidity or dew point — and get the full psychrometric state instantly.
Try it in your browser first: free online psychrometric chart →
Need a paper chart? Printable chart by altitude →
Also available for Android (product page in Turkish):
▶ Android version →The iPhone edition of Psychro Calc Pro puts psychrometric calculation in your pocket. You type two independent properties of moist air on the on-screen keypad, and the app fills in every other quantity in the results table on the same screen. It is aimed at HVAC and industrial process work. The interface is in English, and button names on this page match the app.
The parameter keys are DB °C, WB °C, Dew Point, RH %, Hum. Ratio and Enthalpy (DB °F and WB °F in IP), so you can enter any two different values out of dry bulb, wet bulb, dew point, relative humidity, humidity ratio and enthalpy. The eight rows on the main screen show altitude, dry bulb, wet bulb, dew point, relative humidity, humidity ratio, enthalpy and density. Density cannot be chosen as an input; it is a result only. Altitude is entered separately with the Alt key.
Saturation pressure is calculated with the Hyland–Wexler equations and the water vapor enhancement factor; barometric pressure is derived from altitude. You can read all formulas and references on the About page, opened with the info icon on the main screen. Results are intended for review by a qualified engineer; the app is not a substitute for approval or a certificate of compliance.
Working from a phone usually means taking two readings and asking for a third value: dew point from temperature and relative humidity, or enthalpy from dry- and wet-bulb readings. Enter both values, press ENTER, and the screen shows CALCULATION COMPLETE while the table fills in. The wet bulb is the thermodynamic wet bulb, based on adiabatic saturation. Below 0 °C the dew point is reported as a frost point, because saturation is taken over ice.
The two parameters must differ, and dew point cannot be combined with humidity ratio. Each of those only fixes how much water vapour is in the air. Without a temperature the air state does not settle on a single point, so the app returns no solution. As for ranges, temperatures must stay between −100 and +200 °C, and wet bulb and dew point cannot exceed the dry bulb. If you enter an impossible pair, the message line turns red.
The switch below the results flips between SI (°C) and IP (°F). Turning it keeps your calculation: the values are converted and the result is calculated again; your altitude setting stays too. The results table and the table in the PDF report are written in the selected units. Conversions cover g/kg and gr/lb, kJ/kg and Btu/lb, kg/m³ and lb/ft³, and metres and feet. Saved history is stored in SI and shown in the selected units.
The same temperature and relative humidity measured in a mountain town and on the coast do not give the same answer. As air thins, barometric pressure drops, and humidity ratio and enthalpy depend on that pressure. In Psychro Calc Pro you never type the pressure itself. Saturation pressure is calculated with the Hyland–Wexler equations and the water vapor enhancement factor; barometric pressure is derived from altitude. A value outside the range gives ERR: OUT OF RANGE and the altitude stays as it was.
When an altitude is accepted, the screen shows ALTITUDE SET. It stays in effect while the app is open; when the app is reopened, the altitude is 0 m. Loading an entry from History brings back that calculation's altitude.
Outdoor air at 35 °C and 25 % relative humidity can be calculated at sea level and again at 850 m. Enter 0 m for the first run and 850 m for the second, and the 850 m result shows a higher humidity ratio, because the pressure is lower. Both calculations land in History, and the altitude row tells you which one belongs to which condition.
There is no chart on the iPhone screen; the display is given over to the keypad and the eight-row results table. The chart is produced inside the PDF report instead, with lines of constant relative humidity, enthalpy, wet bulb and specific volume plus the state point you calculated. If you want a zoomable chart on screen, the Mac edition provides one: see Psychro Calc Pro for Mac.
The range of the chart in the PDF is chosen automatically from the point. A dry bulb below −10 °C uses LOW TEMP, above 60 °C uses INDUSTRIAL DRYING, and anything in between uses STANDARD HVAC. The mode name is printed faintly inside the chart. You do not have to pick it yourself.
The PDF key prepares an A4 report containing the app name and version, the unit system, the date, the chart image and a results table with Parameter / Value / Unit columns. The report opens in the system's print and share sheet. If you press the key before calculating, the message line reads CALCULATE FIRST.
With Add Logo you pick an image in the system photo picker (no permission needed), and it is placed in the top-right corner of the report. That way your company identity shows on reports you hand to a client or circulate internally.
This app is not an equipment selection or sizing tool. It finds the properties of one state of moist air. If you want to follow air from one state to another, or work out the mix of two air streams, the separate product Psychro Process Pro is the better fit.
Download the app from its App Store page. It requires iOS 15.0 or later.
On the iPhone the trial starts at first launch and runs for 3 days. While it lasts, a strip at the top of the main screen shows the days remaining. The trial record is held in the device Keychain, so deleting and reinstalling the app does not restart the clock.
When the trial ends, a payment screen offers a one-time Lifetime purchase; the amount appears in the App Store for your country. If you already bought it with the same Apple ID, Restore Purchase gives your access back.
Pick any two different values from dry bulb, wet bulb, dew point, relative humidity, humidity ratio and enthalpy. Dew point and humidity ratio cannot be chosen together. Altitude is set separately with the Alt key and is not part of the pair. Density is never an input; it appears as a calculated result in the table.
Both only describe how much water vapour the air holds and carry no temperature information. Without temperature, the air state cannot be tied to a single point, so the app produces no solution and shows NO SOLUTION. Pair either dew point or humidity ratio with a temperature, relative humidity or wet bulb, and the state can be found.
Temperatures must be between −100 °C and +200 °C. Altitude runs from −500 to 11,000 m, entered in feet if IP is selected. An input outside those limits prints ERR: OUT OF RANGE and is not applied. Press Alt again and type a valid altitude to carry on.
Pressure falls with altitude, and the properties of moist air depend on pressure. Saturation pressure is calculated with the Hyland–Wexler equations and the water vapor enhancement factor; barometric pressure is derived from altitude. A site high above sea level therefore gives different results from the coast for the same temperature and relative humidity. It stays in effect while the app is open; when the app is reopened, the altitude is 0 m.
The main screen is reserved for the results table and keypad, so the chart appears only in the PDF report. Pressing PDF prepares a report with a chart showing the point you calculated. Its range switches automatically between LOW TEMP, STANDARD HVAC and INDUSTRIAL DRYING, depending on the temperature of the point.
On the iPhone the free trial lasts 3 days and begins the first time you open the app. When it ends, the app asks for a one-time Lifetime purchase, paid through the App Store in your country's currency. If you purchased with the same Apple ID before, Restore Purchase brings access back. Reinstalling does not restart the trial.
Yes. Pick an image in the system photo picker with Add Logo (no permission needed), and the logo appears in the top-right corner of the PDF. The report also carries the app version, the selected unit system, the date, the chart and the results table. To swap the logo, choose another image with the same key.
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