Vapor Pressure Converter

Torr (torr)
Millimeters of Mercury (mmHg)
Atmosphere (atm)
Pascal (Pa)
Kilopascal (kPa)
Bar (bar)
Millibar (mbar)
Pounds per square inch (psi)
760.0000
Torr (torr)
Millimeters of Mercury (mmHg)
Atmosphere (atm)
Pascal (Pa)
Kilopascal (kPa)
Bar (bar)
Millibar (mbar)
Pounds per square inch (psi)
A = 8.07131, B = 1730.63, C = 233.426
23.7562 mmHg

Graph will appear here when calculated

The Antoine equation is used: log₁₀(P) = A - B/(C + T) where P is in mmHg and T is in °C

Vapor Pressure Conversion Guide

Vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. It's an important property in thermodynamics and physical chemistry that indicates a substance's evaporation rate.

When the vapor pressure equals the external pressure, the liquid boils. Substances with higher vapor pressures at normal temperatures are considered more volatile. Understanding this concept is essential when working with related metrics like various pressure units or exploring the behavior of gases.

Common units for vapor pressure include:

  • Torr and mmHg: Essentially equivalent (1 torr = 1 mmHg), commonly used in chemistry and medicine
  • Atmosphere (atm): Standard atmospheric pressure at sea level (1 atm = 760 mmHg)
  • Pascal (Pa): SI unit of pressure (1 atm = 101325 Pa)
  • Bar: Metric unit (1 bar = 100 kPa ≈ 0.987 atm)
  • PSI: Pounds per square inch, common in engineering (1 atm ≈ 14.696 psi)

For broader pressure conversions beyond vapor pressure, you might find our online pressure converter and atmospheric pressure converter helpful for your calculations.

The Antoine equation is a semi-empirical relationship between vapor pressure and temperature for pure substances:

log₁₀(P) = A - B/(C + T)

Where:

  • P is the vapor pressure (typically in mmHg)
  • T is the temperature in °C
  • A, B, C are substance-specific coefficients

The equation is accurate for a limited temperature range and different sets of coefficients may be needed for different temperature ranges. For conversions involving thermal properties, you may also explore our thermal conductivity converter.

Unit Conversion:

  1. Enter your value in the input field
  2. Select the unit of your input value
  3. Select the unit you want to convert to
  4. The result will update automatically

Temperature Calculation:

  1. Select a substance from the dropdown
  2. Enter the temperature in °C
  3. Select your desired output unit
  4. Click "Calculate" to get the vapor pressure

Use the precision selector to control decimal places and toggle scientific notation as needed.

Learning Center: Understanding Vapor Pressure

What This Converter Teaches
  • Pressure unit relationships and conversions
  • The connection between temperature and vapor pressure
  • Real-world applications of different pressure units
  • How scientists measure and calculate vapor pressure
Input Value Interpretation

What your numbers mean:

  • 760 mmHg = Standard atmospheric pressure at sea level
  • 100 kPa ≈ Standard atmospheric pressure (close to 1 atm)
  • 23.8 mmHg = Water's vapor pressure at 25°C (room temp)
  • 14.7 psi = Atmospheric pressure at sea level
Unit Meanings in Simple Terms
Torr / mmHg
"How many millimeters a mercury column would rise" - like in old barometers
Atmosphere (atm)
"Normal air pressure at sea level" - your baseline for comparison
Pascal (Pa)
"The scientific standard" - 1 Newton of force on 1 square meter
PSI
"Everyday engineering" - car tires, gas cylinders, scuba tanks
When to Use Each Unit Type
Use This Unit... When Working With... Example
mmHg / Torr Chemistry labs, medicine (blood pressure), vacuum systems Measuring vapor pressure of solvents
atm General chemistry problems, atmospheric science "Express in atmospheres" textbook questions
kPa / Pa Physics problems, engineering calculations (SI system) International research papers
psi Mechanical engineering, industrial applications (US) Pressure cooker settings, tire pressure
bar / mbar Meteorology, European engineering, automotive Weather maps (millibars)
Real-World Examples
Cooking & Boiling

Water boils at 100°C at 1 atm (760 mmHg). At higher altitudes with lower pressure, water boils at lower temperatures.

Weather Forecasting

High pressure systems (∼1020 mbar) bring clear weather. Low pressure (∼980 mbar) often means storms. For accurate measurements, try our atmospheric pressure converter.

Medical Applications

Normal blood pressure is ∼120/80 mmHg. Vacuum tubes use ∼0.1 mmHg for blood collection.

Step-by-Step Conversion Explanation
  1. Choose your starting unit - What unit is your original measurement in?
  2. Find the conversion factor - The tool converts everything to mmHg first (the common reference)
  3. Convert to target unit - Divide your mmHg value by the target unit's factor
  4. Check your answer - Does the result make sense? (e.g., 760 mmHg should equal 1 atm)
Common Student Mistakes
  • Confusing mmHg with cmHg (10× difference!)
  • Forgetting that 1 atm = 101325 Pa exactly (not 100000)
  • Mixing up multiplication and division when converting
  • Using wrong temperature units with Antoine equation (must be °C)
Exam Usage Tips
  • Memorize these 3 key conversions:
    • 1 atm = 760 mmHg = 101.325 kPa
    • 1 bar = 100 kPa = 0.987 atm
    • 1 psi ≈ 51.7 mmHg
  • For multiple choice: Eliminate obviously wrong answers first
  • Show your work: Write conversion factors with units to avoid errors
  • Estimate: 100 kPa ≈ 1 atm, 760 mmHg ≈ 1 atm (quick checks)
Visual Understanding Suggestions
  • Imagine a mercury column: 760 mm tall = 1 atm
  • Picture car tires: 32 psi = about 2.2 atm
  • Think of layers: 1000 mbar = sea level, 500 mbar = halfway up atmosphere
  • Use the graph feature to see how vapor pressure changes with temperature

Q: Why are Torr and mmHg treated as equal?
A: They were defined to be essentially identical (1 Torr = 1/760 atm, 1 mmHg = 1/760 atm). For most practical purposes, they're interchangeable.

Q: What's the difference between absolute and gauge pressure?
A: Absolute pressure includes atmospheric pressure. Gauge pressure is relative to atmosphere. PSI vs PSIA: PSI is usually gauge, PSIA is absolute.

Q: Why does vapor pressure increase with temperature?
A: More molecules have enough energy to escape the liquid. Double the temperature (in Kelvin) doesn't double vapor pressure - it increases exponentially! Our pressure-temperature converter can help illustrate this relationship.

Q: Can vapor pressure be higher than atmospheric pressure?
A: Yes! This is how pressure cookers work. At 121°C, water's vapor pressure is about 2 atm.

Important Notes & Accuracy Disclaimer

For Educational Use: This tool provides accurate conversions for standard conditions. Actual vapor pressures can vary with purity, altitude, and other factors.

Antoine Equation Limits: The Antoine coefficients are valid for specific temperature ranges. Extreme temperatures may require different coefficient sets.

Rounding: 4 decimal places is usually sufficient for classroom work. For precise engineering, consult specialized references.

Last Updated: November 2025 | Conversion formulas verified against NIST standards.

Learning Tip: Practice by converting everyday pressures: car tires (∼32 psi), weather reports (∼1013 mbar), and soda cans (∼4 atm CO₂ pressure).