Psychrometric Calculator
Moist-air properties from four input pairs, altitude or pressure, and two-stream mixing.
Try before you buy.
- Free preview: the rules, dates and checks that apply to your figures, with every computed amount hidden.
- Locked until you unlock it: download and copy.
- Unlock: Premium pass, ₹799 for 30 days or ₹249 for 1 week, a one-time payment that never renews. Unlock: Premium pass, $19.99 for 30 days or $7.99 for 1 week, a one-time payment that never renews.
Ways to unlock shows how to get the full result.
Printing this result is locked in the free preview.
Working
Assumptions and sources
Locked in the free preview. Opens the ways to unlock this result.
Locked in the free preview. Batch runs unlock with a pass.
Locked in the free preview. Query results unlock with a pass.
Results are estimates from the formulas shown, not a professional design or certification. Have a qualified engineer verify anything safety-critical (structures, electrical installations, gas or pressure systems).
About the Psychrometric Calculator
Enter dry-bulb temperature with relative humidity, wet-bulb temperature, dew point or humidity ratio to calculate a complete moist-air state at the entered absolute pressure or estimated standard-atmosphere altitude. SI and IP modes use their own moist-air equations and enthalpy references. Mix two streams by dry-air mass flow and plot their states and balanced mixture on the same pressure-specific chart. The free preview masks figures and shows a marked chart; a Premium pass opens the result, copy, CSV, SVG chart and PDF report.
How to use it
- Choose SI or IP units and the known moist-air input pair, or choose two-stream mixing. Changing units converts the numeric inputs.
- Enter measured absolute pressure when available; use altitude only for an estimated standard-atmosphere pressure.
- Supply dry bulb and the second property; for mixing, give each dry-bulb temperature, relative humidity and dry-air mass flow.
- Review the chart and warnings in the free preview; supersaturated mixtures are rejected because condensation is outside this model.
- Unlock with a Premium pass to copy all properties or download CSV, the standalone SVG chart, and a PDF containing the chart and working.
Examples
Dry bulb 25 degC, relative humidity 80%, absolute pressure 101.325 kPa
Dew point about 21.3094 degC; humidity ratio, enthalpy, wet bulb, density and volume are also calculated.
Equations and assumptions
Humidity ratio W = 0.621945 pv/(p−pv), with saturation vapour pressure from the ASHRAE equations implemented in PsychroLib. Relative humidity is pv/pws(T). SI enthalpy is [1.006T + W(2501 + 1.86T)] kJ/kg dry air; IP enthalpy is [0.240T + W(1061 + 0.444T)] Btu/lb dry air. Adiabatic mixing balances W and h by dry-air mass flow, then recovers dry bulb from h and W. Chart humidity ratio is W×1000 in g/kg or W×7000 in grains/lb.
Sources
Limitations
- Estimate — not a professional HVAC design. Idealised moist air, one common pressure and adiabatic mixing without condensation are assumed.
- Specific enthalpy and specific volume use a dry-air mass basis; density uses total moist-air mass. Do not confuse humidity ratio with specific humidity.
- SI and IP enthalpy use different reference states. Absolute enthalpy is not converted between them by a scale factor alone.
- Exactly dry air has no finite dew point; its wet-bulb solution uses the engine’s numerical humidity-ratio floor. States outside the published formulation are rejected.
- Vapour partial pressure must stay below the entered total pressure. Nonzero states below the engine’s humidity-ratio floor of 0.0000001 are rejected rather than silently changed; invalid chart-curve states are omitted.
- The mixing path connects the entered states and their balanced mixture; it does not model a transient process or water condensation.
Privacy
On this device; its files download once
All entered dimensions, temperatures, labels and schedules stay on your device. PDF fonts and calculation code can download from MySmartCoPilot; inputs are never sent with those downloads.
Frequently asked questions
What do I get without a pass?
Without a pass, Psychrometric Calculator shows the rules, dates and checks that apply to your figures, with every computed amount hidden. Until you unlock it, the result can’t be downloaded or copied. A Premium or Ultimate pass, a one-time payment that never renews, unlocks the full result. The pricing page lists the passes and their prices.
Can I calculate properties at altitude?
Yes, but altitude estimates pressure using a standard atmosphere. Weather and local conditions can change actual pressure; enter a measured absolute pressure for better results.
Why does a mixed-air state sometimes fail?
Mixing can create a supersaturated state. A reliable result would then require a condensation and liquid-water balance, which this model does not guess.
What does one grain per pound mean on the chart?
There are 7000 grains in a pound. The IP chart uses humidity ratio multiplied by 7000; its underlying ratio remains pounds of vapour per pound of dry air.