Water Vapor Pressure
Specific vapor pressure calculation for water at various temperatures
✅ What This Calculator Is & Why It Matters
The Vapor Pressure of Water Calculator provides the exact partial pressure exerted by water vapor at a specific temperature. It is a highly specialized version of the Antoine equation tuned exclusively for H₂O.
Why does it matter? If you collect a gas in a lab (like hydrogen) by bubbling it into an inverted beaker of water, the gas you collect is not pure. It is contaminated with water vapor! To find the pressure of the *dry* hydrogen gas, you must calculate the vapor pressure of water at room temperature and subtract it from the total pressure (Dalton's Law).
✅ The Formula Explained Simply
The Tetens equation is widely used by meteorologists for highly accurate water vapor calculations:
P = 0.61078 × exp[ (17.27 × T) / (T + 237.3) ]
Where P is pressure in kPa and T is temperature in Celsius.
✅ 3-5 Real-World Examples
Example 1: Collecting Gas over Water
You collect oxygen gas at 25°C. Total pressure is 760 mmHg.
Result: Water vapor pressure at 25°C is 23.8 mmHg. The dry oxygen pressure is exactly 736.2 mmHg.
Example 2: Meteorology (Humidity)
Calculating the maximum amount of water the air can hold at 30°C (86°F) vs 10°C (50°F).
Result: The vapor pressure at 30°C is more than double the pressure at 10°C. Hot air holds vastly more moisture.
✅ FAQ Section (Google PAA Targeted)
Does altitude affect the vapor pressure of water?
No! Vapor pressure is an intrinsic property of the liquid dependent *only* on temperature. However, altitude affects atmospheric pressure, which dictates when that vapor pressure will cause the water to boil.
What is Relative Humidity?
Relative humidity is the actual partial pressure of water vapor in your room divided by the maximum possible vapor pressure of water at that exact temperature (which this calculator provides), multiplied by 100.
✅ Pro-Tips for Water Vapor
- Ice Sublimation: Water vapor pressure doesn't stop at 0°C. Ice has a vapor pressure! This is why ice cubes shrink over time if left in a frost-free freezer for months.
✅ Related Calculators
✅ AI Explanation of Results
Our AI automatically outputs the vapor pressure in multiple units (mmHg, kPa, atm, and psi) simultaneously, saving you the hassle of unit conversion during complex gas-law homework problems.
About the Vapor Pressure of Water Calculator
Calculate boiling point elevation, freezing point depression, vapor pressure, or osmotic pressure for solutions using Raoult’s law.
This precision chemistry tool is designed for academic reference, laboratory workflows, and student education. It provides instant, real-time computational results with standard formulas and dimensional analysis inputs.