Calculator
Example Data Table
Example values below are typical saturation vapor pressure values over water using a common meteorological approximation.
| Temperature (°C) | Saturation Vapor Pressure (kPa) | Approximate Phase | Typical Use |
|---|---|---|---|
| 0 | 0.6112 | Water | Reference point near freezing |
| 10 | 1.2279 | Water | Cool air moisture estimates |
| 20 | 2.3383 | Water | Indoor comfort calculations |
| 30 | 4.2451 | Water | Warm weather humidity work |
| 40 | 7.3824 | Water | Drying and heat process estimates |
Formula Used
1) Arden Buck
Over water: es = 6.1121 × exp[(18.678 − T/234.5) × T / (257.14 + T)]
Over ice: es = 6.1115 × exp[(23.036 − T/333.7) × T / (279.82 + T)]
2) Magnus-Tetens
Over water: es = 6.1094 × exp[(17.625 × T) / (243.04 + T)]
Over ice: es = 6.1121 × exp[(22.46 × T) / (272.62 + T)]
3) Tetens
Over water: es = 6.1078 × 10(7.5T / (237.3 + T))
Over ice: es = 6.1078 × 10(9.5T / (265.5 + T))
4) Sonntag
This model uses logarithmic equations in Kelvin and returns pressure in pascals before conversion. It is useful when you want a more rigorous thermodynamic fit.
Here, T is temperature in °C for Buck, Magnus-Tetens, and Tetens. Sonntag uses Kelvin internally. The formulas first produce pressure in hPa or Pa, then the script converts the result to the selected output unit.
How to Use This Calculator
- Enter the temperature value for the main saturation vapor pressure result.
- Select the temperature unit: Celsius, Fahrenheit, or Kelvin.
- Choose a formula model such as Arden Buck or Sonntag.
- Select the surface phase or keep Auto for water above freezing and ice below freezing.
- Pick the output pressure unit you need.
- Set decimal places for display precision.
- Enter range start, range end, and range step to build the graph and result table.
- Press the calculate button to show the result below the header and above the form.
- Use the CSV or PDF buttons to export the generated results.
Answer to the Requested Question
Saturated water vapor at 350 °C is heated at constant pressure
At constant pressure, adding heat to saturated vapor moves it into the superheated region. The vapor is no longer saturated, its temperature rises above 350 °C, and vapor quality is no longer used because the state remains entirely gaseous.
FAQs
1) What is saturation vapor pressure?
It is the pressure exerted by vapor when evaporation and condensation balance at a given temperature. For water, it rises strongly as temperature increases, which is why warm air can hold much more moisture than cold air.
2) Why does saturation vapor pressure increase with temperature?
Higher temperature gives more molecules enough energy to escape the liquid or ice surface. That increases the equilibrium vapor concentration, so the pressure needed for saturation becomes larger.
3) Which formula should I choose?
Arden Buck is a strong general choice for many practical uses. Magnus-Tetens and Tetens are popular approximations. Sonntag is useful when you prefer a more rigorous thermodynamic fit.
4) Should I use water, ice, or Auto?
Use water for temperatures over liquid water, ice for frost or ice surfaces, and Auto when you want the calculator to switch automatically below 0°C and use water at or above 0°C.
5) Are the results exact?
They are high-quality engineering or meteorological estimates, not absolute truths for every condition. Slight differences between formulas are normal because each model is fitted to a different experimental range or purpose.
6) Why do different formulas give slightly different answers?
Each equation uses its own constants, fitting range, and assumptions. The differences are usually small in normal ranges, but they can grow at very low or very high temperatures.
7) Can I use this calculator for HVAC and weather work?
Yes. Saturation vapor pressure is widely used in HVAC, meteorology, drying, evaporation studies, psychrometrics, and humidity calculations. Choose a suitable formula and unit system for your application.
8) What happens when saturated vapor is heated at constant pressure?
It becomes superheated vapor. The state leaves the saturation line, the temperature rises above the saturation temperature for that pressure, and quality is no longer defined.