Enter temperature, units, and plotting range
Sample propane saturation pressures
| Temperature (°C) | Temperature (°F) | Pressure (bar abs) | Pressure (kPa abs) | Pressure (psi abs) |
|---|---|---|---|---|
| -40 | -40 | 1.1004 | 110.04 | 15.961 |
| -20 | -4 | 2.4434 | 244.34 | 35.439 |
| 0 | 32 | 4.7631 | 476.31 | 69.084 |
| 20 | 68 | 8.4043 | 840.43 | 121.895 |
| 40 | 104 | 13.7396 | 1373.96 | 199.276 |
Generalized vapor-pressure relation
Main equation: ln(Psat/Pc) = f0(Tr) + ω f1(Tr)
Reduced temperature: Tr = T / Tc
Functions:
f0 = 5.92714 − 6.09648/Tr − 1.28862 ln(Tr) + 0.169347 Tr6
f1 = 15.2518 − 15.6875/Tr − 13.4721 ln(Tr) + 0.43577 Tr6
Propane properties used: Tc = 369.83 K, Pc = 42.48 bar, ω = 0.152
Gauge pressure is estimated as Pgauge = Pabsolute − 1 atm.
This approach is practical for engineering estimates over a broad temperature range below the critical point. Results near the critical region become more sensitive.
Steps for quick and consistent use
- Enter the propane temperature using Celsius, Fahrenheit, or Kelvin.
- Choose the pressure unit you want for reporting or comparison.
- Select whether the headline result should emphasize absolute or gauge pressure.
- Define a range start, end, and step to build the results table.
- Press the calculate button to show the result summary above the form.
- Review the graph, then export the generated table as CSV or PDF.
- For critical equipment decisions, compare the estimate against your approved property reference.
Frequently asked questions
1) What does this calculator estimate?
It estimates propane saturation pressure at a chosen temperature. That means the equilibrium vapor pressure of propane when liquid and vapor phases can coexist.
2) Why does vapor pressure rise with temperature?
As temperature increases, propane molecules have more energy to escape the liquid phase. That raises the equilibrium pressure needed to balance evaporation and condensation.
3) What is the difference between absolute and gauge pressure?
Absolute pressure is referenced to a perfect vacuum. Gauge pressure is referenced to local atmosphere, so it is approximately absolute pressure minus one atmosphere.
4) Is the result valid at the critical point?
No. At the critical point, liquid and vapor become indistinguishable. This calculator is intended for temperatures below propane’s critical temperature of 369.83 K.
5) Can I use the result for tank design approval?
Use it for screening, training, and quick checks. Final design, compliance, and relief studies should rely on approved property data and the governing code requirements.
6) Why can gauge pressure become negative?
If the calculated absolute pressure is below atmospheric pressure, subtracting one atmosphere gives a negative gauge value. That can happen at low temperatures.
7) Which pressure unit should I choose?
Choose the unit used in your operating documents or instruments. kPa, bar, and psi are common for process work, while atm and mmHg help with comparisons.
8) Why export the table instead of only reading the headline result?
A temperature range shows how quickly pressure changes. That is useful for operating envelopes, training material, equipment reviews, and handoff documentation.