Input parameters
Calculated results
Each calculation is added to the table so you can compare multiple temperatures.
| # | Temperature (input) | Temperature (K) | Pressure (bar) | Pressure (kPa) | Pressure (atm) |
|---|
Example ammonia vapor pressure values
These sample values are generated from the same Antoine correlation used in the calculator and provide quick reference at common temperatures.
| Temperature (°C) | Temperature (K) | Pressure (bar) | Pressure (kPa) | Pressure (atm) | Pressure (mmHg) |
|---|---|---|---|---|---|
| -40 | 233.15 | 0.728 | 72.78 | 0.718 | 545.9 |
| -20 | 253.15 | 1.905 | 190.50 | 1.880 | 1428.9 |
| 0 | 273.15 | 4.258 | 425.81 | 4.202 | 3193.8 |
| 20 | 293.15 | 8.494 | 849.40 | 8.383 | 6371.0 |
| 40 | 313.15 | 15.466 | 1546.62 | 15.264 | 11600.6 |
Formula used for ammonia vapor pressure
This calculator uses the Antoine equation in the form log10(P) = A − B / (T + C), where P is the vapor pressure in bar and T is temperature in kelvin.
Antoine parameters for ammonia are taken from correlations based on Stull data:
- 164.0–239.6 K: A = 3.18757, B = 506.713, C = −80.78
- 239.6–371.5 K: A = 4.86886, B = 1113.928, C = −10.409
For temperatures outside this range, the tool still provides a result by extrapolating with the nearest parameter set, but the reliability decreases and should be treated cautiously.
How to use this calculator
- Enter the process temperature in your preferred unit (°C, K, or °F).
- Click “Calculate vapor pressure” to compute saturation pressure.
- Each new calculation is appended to the results table for comparison.
- Use “Clear table” to reset the results area when needed.
- Click “Download CSV” to export the table data to a spreadsheet.
- Click “Download PDF” to archive a compact report of your calculations.
Always verify that your operating temperature lies within the recommended Antoine range for the highest confidence in the predicted vapor pressure.
Understanding ammonia vapor pressure
Ammonia is widely used as a refrigerant, fertilizer precursor, and industrial feedstock. Its vapor pressure curve strongly influences equipment design, storage conditions, and safety envelopes. Saturation pressure defines the equilibrium between liquid and vapor phases at a given temperature. Accurate vapor pressure values allow engineers to size piping, valves, and compressors and to estimate loads on condensers, evaporators, and storage tanks. This calculator focuses specifically on pure anhydrous ammonia under equilibrium conditions.
Antoine equation parameters for ammonia
The Antoine equation offers a compact way to describe vapor pressure as a function of temperature using three empirical constants. For ammonia, separate parameter sets are recommended for low and moderate temperatures, capturing behavior from cryogenic regions up to near the normal boiling point. Within the specified ranges, errors are typically small compared with experimental uncertainties. Outside these ranges, extrapolation becomes less reliable, so users should compare results with trusted tables when making critical decisions.
Temperature ranges and units in this tool
The underlying correlation expects temperature in kelvin, but process data are often recorded in Celsius or Fahrenheit. The calculator handles conversions automatically before evaluating the Antoine equation. It also reports vapor pressure in several convenient units, including bar, kilopascal, and standard atmospheres. This flexibility helps you align results with your plant standards, simulation software, or instrument readings without manual conversion.
Design and safety applications
In refrigeration systems, ammonia vapor pressure determines suction and discharge levels for compressors and influences selection of pressure ratings for vessels. In storage applications, knowledge of saturation pressure across seasonal temperatures supports vent sizing, relief setting, and insulation choices. Process safety teams often trace worst-case scenarios using conservative temperature assumptions and corresponding vapor pressures. A fast calculator like this one helps iterate scenarios during hazard studies and early design reviews.
Comparing with tabulated vapor pressure data
Many handbooks publish discrete tables of ammonia vapor pressure versus temperature. While useful, they require interpolation and can be cumbersome when exploring many conditions. This calculator recreates the same behavior with continuous correlations, enabling quick sweeps across temperature ranges. When high accuracy is essential, you can still benchmark selected points against published tables to confirm the chosen parameter set remains appropriate for your operating window.
Related chemistry calculators for deeper analysis
Ammonia is rarely the only fluid of interest in real systems. For comparisons across different refrigerants or gases, you might pair this page with tools such as a propane vapor pressure calculator or a CO₂ partial pressure calculator. Combining results lets you evaluate alternative working fluids, examine mixture behavior qualitatively, and understand how ammonia compares to hydrocarbons and other common process gases used in your facility.
Best practices and limitations
Although the Antoine correlation provides fast estimates, it does not capture effects such as impurities, non-ideal mixtures, or very high pressures near the critical region. For rigorous design, especially in mixed streams, an equation of state or dedicated property package is more appropriate. Nonetheless, this calculator is ideal for quick checks, preliminary sizing, and educational use. Recording results via CSV or PDF exports ensures your assumptions remain transparent and easy to revisit as designs evolve.
Frequently asked questions
1. What is ammonia vapor pressure?
Ammonia vapor pressure is the equilibrium pressure exerted by ammonia vapor above its liquid at a given temperature. It defines when liquid and vapor coexist and strongly influences refrigeration performance, storage tank design, and safety margins.
2. Which temperature range is supported by this calculator?
The Antoine parameters are recommended between roughly 164 and 371.5 kelvin. The tool can extrapolate outside this window, but results should be treated as estimates and checked against reliable tables or property packages for critical design decisions.
3. Which units are used for the pressure results?
Internally, the correlation returns vapor pressure in bar. The calculator converts this value into kilopascals and standard atmospheres for convenience. You can easily translate these units into others, like pounds per square inch, using standard conversion factors.
4. How accurate is the Antoine equation for ammonia?
Within the published temperature range, the Antoine equation usually matches experimental data closely enough for engineering estimates. Accuracy decreases when extrapolating or when impurities, dissolved gases, or mixtures significantly affect phase behavior. For critical work, compare with trusted thermodynamic databases.
5. Can I export my ammonia vapor pressure calculations?
Yes. After performing one or more calculations, you can export the results table as a CSV file suitable for spreadsheets, or generate a simple PDF summary. These exports help document design assumptions, share results with colleagues, or archive study notes.
6. When should I avoid extrapolating beyond the Antoine range?
Avoid extrapolation near the critical region, at extremely low temperatures, or whenever equipment ratings, safety relief sizing, or regulatory documentation depend on precise values. In those cases, rely on high-quality thermophysical data or advanced property models that cover the required conditions explicitly.