Calculator
Example Data Table
| Case | Air Temp | RH | Dew Point | Saturation Pressure | Actual Pressure |
|---|---|---|---|---|---|
| Warm indoor air | 25 °C | 60 % | 16.7 °C | 31.67 hPa | 19.00 hPa |
| Cool storage room | 10 °C | 55 % | 1.4 °C | 12.26 hPa | 6.74 hPa |
| Greenhouse target | 30 °C | 70 % | 23.9 °C | 42.34 hPa | 29.64 hPa |
Formula Used
Saturation vapor pressure: es(T) is calculated from the selected equation family. The page supports Magnus, Tetens, and Arden Buck forms for water or ice.
Actual vapor pressure from relative humidity: e = RH / 100 × es(T)
Actual vapor pressure from dew point: e = es(Td)
Relative humidity from dew point: RH = 100 × e / es(T)
Vapor pressure deficit: VPD = es(T) − e
Dew point estimation: the page uses a numeric search to find the temperature where saturation vapor pressure matches the actual vapor pressure.
How to Use This Calculator
- Choose a calculation mode.
- Pick an equation family and surface type.
- Enter air temperature and choose its unit.
- Add relative humidity, dew point, or both when needed.
- Select the output pressure unit and decimal places.
- Press Calculate to show the result above the form.
- Use the CSV button for spreadsheet records.
- Use the PDF button to print or save a report.
About Vapor Pressure and Saturation Vapor Pressure
What These Values Mean
Vapor pressure describes how strongly a liquid escapes into air. Saturation vapor pressure shows the maximum pressure possible at a given temperature. This calculator helps you study both values together. It also estimates dew point, relative humidity, and vapor pressure deficit. Those outputs support weather work, storage checks, drying analysis, and lab review.
Why Temperature Matters
Temperature drives most vapor pressure changes. Warmer air can support more water vapor. That is why saturation vapor pressure rises quickly with heat. Actual vapor pressure depends on available moisture. When actual pressure reaches the saturation limit, condensation can begin. This relationship explains fog, dew, cloud growth, and surface moisture changes.
Why Formula Choice Matters
The calculator lets you choose common equations. Magnus is popular for everyday estimation. Tetens is simple and widely taught. Arden Buck often gives refined values across practical ranges. You can also switch between water and ice surfaces. That matters in cold environments. Ice and water do not share the same saturation behavior.
Why Flexible Inputs Help
Unit options make comparison easier. Enter temperature in Celsius, Fahrenheit, or Kelvin. View pressure in hPa, kPa, Pa, or mmHg. You can test one condition or compare several assumptions. The result block appears above the form after submission. That layout keeps the answer in view while you adjust fields below.
Best Ways to Use It
Use the saturation mode when you only need the moisture limit at one temperature. Use the relative humidity mode when temperature and humidity are known. Use the dew point mode when temperature and dew point are available. The full compare mode helps check agreement between relative humidity and dew point inputs. That is useful during validation work.
Why the Export Tools Matter
Downloaded CSV files support record keeping. The PDF option helps with printing and sharing. The example table on this page shows realistic sample conditions. The formula section explains what the calculator does internally. The how to use section gives a quick workflow. Together, these parts make the page useful for students, engineers, technicians, and analysts who need quick and repeatable moisture calculations.
Why This Page Stays Practical
Because the page uses a single file structure, setup stays simple. You can place it on a standard server and run calculations without extra configuration. Minimal styling keeps the layout clean. Responsive fields still organize inputs well on large, medium, and small screens for tasks.
FAQs
1. What is saturation vapor pressure?
Saturation vapor pressure is the highest water vapor pressure air can support at a specific temperature. If actual vapor pressure reaches that level, condensation can start.
2. What is actual vapor pressure?
Actual vapor pressure is the pressure created by water vapor that is already present in the air. It is usually lower than the saturation value.
3. Why does the calculator offer several formulas?
Different formulas are common in weather, engineering, and teaching work. The options help you compare methods and match the approach used in your project.
4. When should I choose ice instead of water?
Choose ice when you want saturation behavior over an ice surface. This is useful in freezing conditions, frost studies, and cold weather analysis.
5. What is vapor pressure deficit?
Vapor pressure deficit is the gap between saturation vapor pressure and actual vapor pressure. It shows drying demand and is useful in plant and storage work.
6. Can I calculate dew point from humidity here?
Yes. In relative humidity mode, the calculator estimates dew point from actual vapor pressure and the selected equation family.
7. What does the full comparison mode do?
It compares actual vapor pressure from relative humidity with actual vapor pressure from dew point. This helps you spot input mismatch or measurement drift.
8. How does the PDF button work?
The PDF button opens a printable report view in your browser. From there, you can save the page as a PDF file.