Calculator inputs
Formula used
P = Pc × exp[(Tc/T) × Σ(niθti)]
θ = 1 − T/Tc
log10(Pbar) = A − B/(T + C)
ln(Pr) = f(0)(Tr) + ωf(1)(Tr)
Pgauge = Pabsolute − Patmosphere
The reference method uses Tc = 369.89 K and Pc = 4.2512 MPa. Reduced temperature is Tr = T/Tc, while reduced pressure is Pr = P/Pc.
How to use this calculator
- Select pressure, reverse temperature, table, or comparison mode.
- Choose a correlation and enter the required temperature or pressure.
- Select units, atmospheric conditions, precision, and display notation.
- Press Calculate, then review validity messages and detailed steps.
- Export the result, table, chart, or printable PDF report.
Use the automatic method for the widest pure-propane range. Use Antoine only inside its displayed coefficient interval.
Example data
| Temperature | Approximate absolute pressure | Typical interpretation |
|---|---|---|
| -40 °C | 1.1113 bar | Severe cold |
| 0 °C | 4.7443 bar | Freezing conditions |
| 20 °C | 8.3637 bar | Room temperature |
| 40 °C | 13.6938 bar | Hot weather |
| 80 °C | 31.3191 bar | High-temperature region |
Understanding propane vapor pressure
Propane vapor pressure is the equilibrium pressure above liquid propane at a fixed temperature. It rises quickly as temperature increases because more liquid molecules enter the vapor phase. The value assumes pure propane has reached thermal equilibrium.
A partially filled cylinder can show nearly the same equilibrium pressure as a fuller cylinder. Fill level mainly changes the available liquid reserve and expansion space. Temperature and composition control equilibrium pressure much more directly.
Absolute pressure is measured from a perfect vacuum. Gauge pressure subtracts the surrounding atmospheric pressure from that absolute value. Local elevation therefore changes a gauge reading without changing saturation pressure.
Commercial LPG can contain butane, propylene, ethane, and other components. Such mixtures may produce pressures different from pure-propane calculations. Certified supplier data should guide regulated equipment and storage decisions.
Antoine coefficients provide convenient results within their fitted temperature intervals. The Wagner-type ancillary covers the propane saturation curve much more broadly. Lee–Kesler provides a useful corresponding-states comparison for engineering screening.
Above the critical temperature, liquid and vapor cannot remain distinct equilibrium phases. A conventional saturation pressure therefore has no physical meaning there. Use a suitable equation of state for supercritical conditions.
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Frequently asked questions
What controls propane cylinder pressure?
Temperature and fluid composition primarily control equilibrium pressure when liquid propane remains present.
Does a fuller cylinder always have higher pressure?
No. At equal temperature and composition, equilibrium vapor pressure is nearly independent of fill level.
What is the difference between psia and psig?
Psia is absolute pressure. Psig is pressure above the selected local atmospheric pressure.
Why can LPG differ from this result?
LPG mixtures can include butane and other hydrocarbons that alter equilibrium pressure.
Which method should I choose?
The automatic Wagner-type reference method offers the broadest embedded pure-propane range.
Why is Antoine sometimes unavailable?
Each Antoine coefficient set is fitted only across a specific temperature interval.
Can vapor pressure be calculated above the critical temperature?
No distinct liquid–vapor saturation pressure exists above propane’s critical temperature.
Does elevation change absolute vapor pressure?
No. Elevation changes atmospheric and gauge pressure, not pure-fluid absolute saturation pressure.
Can this calculator set relief valves?
No. Use applicable codes, certified data, approved equipment, and qualified engineering review.