Pressure Conversions: From PSI to Pascals | EazyUnit Blog: Unit Conversion, Measurement, and Science

Introduction to Pressure

Pressure is defined as force per unit area, and it's measured in various units depending on the field and region. From tire pressure in PSI to scientific measurements in pascals, understanding pressure conversions is essential for engineers, scientists, mechanics, and anyone working with pressurized systems.

This guide covers the most common pressure units and how to convert between them accurately.

Fundamental Pressure Units

Pascal (Pa)

The pascal is the SI unit of pressure, named after Blaise Pascal:

• 1 Pa = 1 N/m² (newton per square meter)
• 1 Pa = 0.000145038 PSI
• 1 Pa = 0.00001 bar

The pascal is relatively small, so larger units are commonly used:

• 1 kilopascal (kPa) = 1,000 Pa
• 1 megapascal (MPa) = 1,000,000 Pa

PSI (Pounds per Square Inch)

PSI is commonly used in the United States for:

• Tire pressure
• Hydraulic systems
• Compressed air systems
• Scuba diving

Conversions:

• 1 PSI = 6,894.76 Pa ≈ 6,895 Pa
• 1 PSI = 0.0689476 bar
• 1 PSI = 0.068046 atmospheres

Bar

The bar is commonly used in Europe and for meteorological pressure:

• 1 bar = 100,000 Pa = 100 kPa
• 1 bar = 14.5038 PSI
• 1 bar = 0.986923 atmospheres

Millibar (mbar) is also common: 1 bar = 1,000 mbar

Atmosphere (atm)

Standard atmosphere is based on average sea-level pressure:

• 1 atm = 101,325 Pa = 101.325 kPa
• 1 atm = 14.6959 PSI
• 1 atm = 1.01325 bar

This is approximately the pressure at sea level on Earth.

Torr and mmHg

Used in vacuum systems and medical applications:

• 1 torr = 1 mmHg (millimeters of mercury)
• 1 torr = 133.322 Pa
• 1 torr = 0.0193368 PSI
• 760 torr = 1 atmosphere

Conversion Table

Practical Applications

Tire Pressure

Tire pressure is typically measured in PSI (US) or bar (Europe):

• Typical car tire: 30-35 PSI = 2.07-2.41 bar
• Bicycle tire: 60-100 PSI = 4.14-6.89 bar
• Truck tire: 80-120 PSI = 5.52-8.27 bar

Always check your vehicle's recommended pressure in the correct units.

Scuba Diving

Divers work with pressure in various contexts:

• Surface pressure: ~14.7 PSI = 1 atm = 1.013 bar
• Every 33 feet of depth adds 1 atmosphere of pressure
• At 66 feet: 3 atm total pressure

Weather and Meteorology

Atmospheric pressure is measured in various units:

• Standard sea-level pressure: 1013.25 mbar = 101.325 kPa = 29.92 inHg
• High pressure: Above 1020 mbar
• Low pressure: Below 1000 mbar

Engineering Applications

Engineers use pressure units for:

• Hydraulic systems: Typically 1,000-5,000 PSI
• Pneumatic systems: Typically 80-120 PSI
• Boiler pressure: Measured in PSI or bar
• Vacuum systems: Measured in torr or mmHg

Learn more about engineering conversions in our comprehensive guide.

Conversion Methods

Using Pascal as Reference

Convert everything to pascals first, then to your target unit:

1. Convert source unit to pascals
2. Convert pascals to target unit

Example: Convert 50 PSI to bar

• 50 PSI × 6,895 Pa/PSI = 344,750 Pa
• 344,750 Pa ÷ 100,000 Pa/bar = 3.4475 bar

Direct Conversion Factors

For common conversions, memorize key factors:

• PSI to bar: Multiply by 0.0689
• Bar to PSI: Multiply by 14.5
• PSI to kPa: Multiply by 6.895
• kPa to PSI: Divide by 6.895

Common Pressure Ranges

Understanding typical pressure ranges helps with conversions:

• Vacuum: Less than 1 atm (measured in torr or mmHg)
• Atmospheric: ~1 atm = 14.7 PSI = 101.3 kPa
• Low pressure: 1-100 PSI (pneumatic systems)
• Medium pressure: 100-1,000 PSI (hydraulic systems)
• High pressure: 1,000+ PSI (industrial applications)

Altitude and Pressure

Atmospheric pressure decreases with altitude:

• Sea level: ~101.3 kPa = 14.7 PSI = 1 atm
• 1,000 m (3,280 ft): ~90 kPa = 13.0 PSI
• 5,000 m (16,400 ft): ~54 kPa = 7.8 PSI

This affects cooking, breathing, and equipment performance at high altitudes.

Tips for Accurate Conversions

1. Use pascals as intermediate: Convert via pascals for accuracy
2. Check your context: Different fields use different units
3. Account for gauge vs. absolute: Gauge pressure excludes atmospheric pressure
4. Use conversion tools: Online calculators ensure accuracy
5. Verify significant figures: Match precision to your application

Gauge vs. Absolute Pressure

Important distinction:

• Gauge pressure: Pressure relative to atmospheric pressure (what most gauges show)
• Absolute pressure: Total pressure including atmospheric pressure

Absolute Pressure = Gauge Pressure + Atmospheric Pressure

Example: A tire at 35 PSI gauge = 35 + 14.7 = 49.7 PSI absolute

Conclusion

Mastering pressure conversions is essential for anyone working with pressurized systems, from automotive applications to scientific research. Understanding the relationships between PSI, pascals, bar, and atmospheres helps you work confidently across different measurement systems.

Remember to use appropriate units for your context, account for gauge vs. absolute pressure, and always verify conversions, especially for safety-critical applications.