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BTU Logic

Tools / Psychrometric Calculator

Psychrometric Calculator

A free psychrometric calculator that runs in your browser, in IP (°F) or SI (°C) units, with no sign-up. Enter dry-bulb plus one other property and get the full air state, plotted on a psychrometric chart drawn at your site’s barometric pressure. It also mixes two airstreams and works out the load across a coil.

  • IP (°F) or SI (°C) units; switching converts the numbers already entered
  • Dry-bulb plus relative humidity, wet-bulb, dew point, humidity ratio, or enthalpy
  • Full air state: wet-bulb, dew point, relative humidity, humidity ratio, enthalpy, specific volume
  • Site elevation sets the barometric pressure for both the numbers and the chart
  • Mixing: two airstreams blended by airflow, flagged if the mix lands past saturation
  • Coil load: total, sensible, and latent load, sensible heat ratio, and condensate
  • Every state plotted on the chart; results download as CSV
  • ASHRAE Handbook—Fundamentals, Chapter 1 relations (Hyland–Wexler saturation pressure)
Air-property results follow the psychrometric relations and assumptions built into this tool (and any inputs you enter). Not a substitute for lab measurement, manufacturer data, or licensed HVAC design. Verify before using in calculations that affect equipment selection or comfort/safety.

Barometric pressure 29.921 in. Hg from the standard atmosphere. Every property except dry-bulb shifts with it.

Air state

Air state

Dry-bulb80.00 °F
Wet-bulb67.00 °F
Dew point60.31 °F
Relative humidity51.1 %
Humidity ratio78.2 gr/lb
Enthalpy31.47 Btu/lb
Specific volume13.8495 ft³/lb
Density0.0730 lb/ft³
Degree of saturation50.2 %
Vapor pressure7.174 in. w.c.

Relations follow ASHRAE Handbook — Fundamentals, Chapter 1: the Hyland–Wexler saturation-pressure correlation, with the chapter’s perfect-gas relations for humidity ratio, enthalpy, specific volume and wet-bulb. Those relations hold to better than about 0.7% from −58 to 122 °F (−50 to 50 °C); between there and the 158 °F (70 °C) ceiling they still solve but the result is flagged as approximate, and past the ceiling they are too coarse to report. ASHRAE RP-1485 (2009) real-fluid properties differ by a few tenths of a percent. Enter dry-bulb plus one other property; every practical pairing includes dry-bulb.

Psychrometric chart

Dry-bulb vs. humidity ratio at the site pressure. Saturation and RH guides use the same solver as the tables.

State20%40%60%80%32405060708090100110020406080100120140160180Dry-bulb (°F)Humidity ratio (gr/lb)
Air state at 80.0 °F, 78.2 gr/lb

Utility only — not a PE stamp, certified weather product, or code-approved calculation. Outputs are estimates from your inputs/files; verify before design, bidding, or compliance use. Terms