Calculator
Formula Used
This calculator uses the Antoine equation, a practical vapor pressure correlation:
To find a boiling point at a given pressure, the equation is rearranged:
Constants are most reliable inside their published temperature range.
How to Use
- Select a calculation mode for boiling point or pressure.
- Choose a fluid preset, or select Custom for your constants.
- Enter the known value and pick the correct input units.
- Choose output units for clear reporting and comparison.
- Click Calculate to display results above the form.
- Use CSV or PDF buttons to export the computed summary.
Example Data Table
Typical water boiling points at selected pressures.
| Pressure (kPa) | Approx. Boiling Point (°C) | Typical Use Case |
|---|---|---|
| 50 | 81.4 | Low-pressure evaporation and vacuum systems |
| 101.325 | 100.0 | Standard atmospheric conditions |
| 200 | 120.2 | Pressurized heating and closed-loop processes |
For best accuracy, use the same constant basis as your reference.
1) Why boiling point changes with pressure
A liquid boils when its vapor pressure equals the surrounding pressure. Lower pressure requires less vapor pressure, so boiling occurs at a lower temperature. Higher pressure raises the required vapor pressure, increasing the boiling point. For reference, standard pressure is 101.325 kPa, which equals 1 atm and 760 mmHg.
2) What the calculator computes
The tool can calculate boiling point from pressure or compute vapor pressure from temperature. Results can be displayed in °C, K, or °F, and pressure outputs can be shown in kPa, bar, atm, mmHg, or psi. The unit conversion is handled internally so the underlying vapor pressure equation remains consistent.
3) Data you can sanity-check quickly
Water is a familiar benchmark: at 101.325 kPa, boiling is 100.0 °C. At 50 kPa, boiling drops to about 81.4 °C, while at 200 kPa it increases to about 120.2 °C. These numbers help validate your inputs before exporting results.
4) The Antoine correlation in practical work
The Antoine equation is widely used for engineering estimates because it is fast and reasonably accurate within a stated temperature range. It models the logarithm of pressure, so small changes in temperature can cause noticeable pressure shifts, especially near a fluid’s normal boiling region.
5) Choosing reliable constants
Each fluid has multiple published constant sets, often tailored to a temperature window. For example, a set valid from 1–100 °C is excellent for near-ambient water calculations, but it may be unreliable far outside that range. When using a custom fluid, keep A, B, and C from the same source and avoid mixing datasets.
6) Pressure units and measurement context
Use absolute pressure for boiling calculations. If you measure gauge pressure, convert it by adding local atmospheric pressure first. A common mistake is using gauge readings directly, which can underpredict boiling temperature under pressurized conditions or overpredict it under vacuum.
7) Interpreting results for design and safety
Boiling point influences flashing risk, cavitation margins, and heat-transfer performance. In process work, a 10–20 kPa change in operating pressure can shift boiling temperature by several degrees for many liquids, affecting control setpoints and equipment limits. Always confirm with verified property data for final design.
8) Exporting and reporting
After calculation, export a CSV summary for spreadsheets or download a PDF for sharing. The exported report includes the selected mode, fluid, units, and constants used. This makes review easier and helps maintain traceability in lab notes, audits, and operating logs.
FAQs
1) Is the pressure input absolute or gauge?
Use absolute pressure. If you only have gauge pressure, add local atmospheric pressure before calculating boiling point.
2) Why does the calculator use mmHg internally?
The Antoine equation is commonly published with pressure in mmHg and temperature in °C, so conversions keep the equation consistent while you freely choose display units.
3) Can I trust results outside the listed temperature range?
Treat them as rough estimates. Antoine constants are fitted for specific ranges, and accuracy can degrade quickly outside those limits.
4) What should I do if I have different constants from a handbook?
Select Custom and enter your A, B, and C exactly as published. Keep the units consistent with that source.
5) Why can’t I download CSV/PDF before calculating?
Exports are enabled only after a valid result is generated, so the file always contains a complete and traceable calculation summary.
6) Does composition affect boiling point at a given pressure?
Yes. Mixtures may boil over a range and can deviate strongly from pure-fluid behavior. Use mixture property models for accurate work.
7) Which mode should I use for vacuum distillation planning?
Use “Boiling point from pressure” to estimate boiling temperature at your vacuum setpoint, then validate against reliable property data.