CO2 (R744) pressure temperature chart (PT)
A CO2 (R744) pressure temperature chart (PT chart) is a saturation lookup for CO2 below the critical point: it relates temperature and saturation pressure when liquid and vapor coexist in equilibrium. This can be helpful for thermodynamic interpretation — but CO2 systems often operate near (or above) the critical point, so PT-chart intuition must be used carefully.
Critical point warning (important for CO2)
CO2 has a relatively low critical temperature (about 30.98°C). Above the critical point, there is no saturation pressure/temperature relationship — so a PT chart does not apply in the supercritical/transcritical region. Many CO2 refrigeration and heat pump cycles use a gas cooler (transcritical operation) where “condensing temperature” is not defined.
For background, see Critical point and Refrigerant PT chart.
Pressure basis: absolute vs gauge
The table below is absolute pressure (kPa(a), bar(a), psi(a)). Many gauges display gauge pressure (relative to ambient). Converting requires local atmospheric pressure:
Learn more: Gauge vs absolute pressure (psig vs psia).
CO2 pressures can be high. This page is educational and is not a repair or operating guide — always follow OEM procedures and safety requirements.
CO2 saturation pressure vs temperature (reference table)
Generated using CoolProp (the same property engine used by FluidTool) at Q=0 saturation. The table is limited to temperatures below the critical point.
| T (°C) | T (°F) | Psat (kPa(a)) | Psat (bar(a)) | Psat (psi(a)) |
|---|---|---|---|---|
| -20 | -4 | 1969.6 | 19.696 | 285.7 |
| -10 | 14 | 2648.7 | 26.487 | 384.2 |
| 0 | 32 | 3485.1 | 34.851 | 505.5 |
| 10 | 50 | 4502.2 | 45.022 | 653.0 |
| 20 | 68 | 5729.1 | 57.291 | 830.9 |
| 30 | 86 | 7213.7 | 72.137 | 1046.3 |
How to verify any row in FluidTool
- Open FluidTool with CO2 selected: /?fluid=CO2
- Choose a Two-phase input pair (Temperature & Quality / T + Q).
- Set Q=0 and enter the temperature from the table to read Psat.
For transcritical operation, PT saturation is not the right mental model for the high side — use the full state (P+T) and look at supercritical properties instead.
Related
- CO2 (R744) data sheet: basic identifiers and thermodynamic context.
- Car A/C pressure chart: why “normal pressures” vary and what PT charts can/can’t tell you.
- R1234yf PT chart: a saturation reference for a common automotive refrigerant.
- R134a PT chart: a saturation reference for R134a.