Pressure Converter - Convert Pascal, Bar, PSI, ATM Online

Convert between any pressure unit with our free online pressure converter. Covers pascals, bar, PSI, atmospheres, mmHg, and more for science, engineering, and weather applications.

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Understanding Pressure Units

Pressure measures force applied over an area. Different fields use different units: scientists prefer pascals (the SI unit), engineers often use PSI or bar, meteorologists use millibars or inches of mercury, and medical professionals use mmHg for blood pressure.

Understanding how to convert between these units is essential for reading international specifications, comparing equipment ratings, and interpreting scientific data from different sources.

Common Pressure Units Explained

Pascal (Pa)

The SI unit of pressure, named after Blaise Pascal.

1 Pa = 1 N/m² (one newton per square meter)

Very small unit - atmospheric pressure is ~101,325 Pa

Bar

Metric unit, convenient for atmospheric pressures.

1 bar = 100,000 Pa = 0.9869 atm

Common in Europe for tire pressure and weather

PSI (lb/in²)

Pounds per square inch - Imperial/US unit.

1 psi = 6,894.76 Pa

Used for tire pressure, scuba tanks, hydraulic systems

Atmosphere (atm)

Based on average sea-level atmospheric pressure.

1 atm = 101,325 Pa = 14.696 psi

Convenient reference point for many applications

mmHg / Torr

Millimeters of mercury - based on mercury column height.

1 mmHg = 1 Torr = 133.322 Pa

Used for blood pressure and vacuum measurements

Kilopascal (kPa)

1,000 pascals - more practical than Pa alone.

1 kPa = 1,000 Pa = 0.145 psi

Common in automotive and HVAC applications

Worked Examples

Example 1: Tire Pressure Conversion

Your car manual specifies 32 PSI, but your gauge reads in bar. What should you set?

32 PSI to bar

32 psi × 0.0689476 bar/psi = 2.206 bar

Set your tires to 2.21 bar

Example 2: Blood Pressure Reading

A blood pressure of 120/80 mmHg - what is this in other units?

Systolic (120 mmHg):

120 mmHg = 120 Torr = 15,999 Pa = 15.999 kPa = 2.32 psi

Diastolic (80 mmHg):

80 mmHg = 80 Torr = 10,666 Pa = 10.666 kPa = 1.55 psi

Normal blood pressure is about 0.16/0.11 atm

Example 3: Scuba Diving

A scuba tank is filled to 200 bar. What's this in PSI?

200 bar to psi

200 bar × 14.5038 psi/bar = 2,900.76 psi

The tank pressure is about 2,901 PSI

At 30m depth (4 atm), you'd have ~50x that pressure outside!

Example 4: Weather Pressure

A weather report shows 1013.25 millibars. Convert to inches of mercury.

1013.25 mbar = 101.325 kPa = 1 atm

1 atm = 760 mmHg = 29.92 inches Hg

Standard atmospheric pressure: 29.92 inHg

Quick Fact

Evangelista Torricelli invented the barometer in 1643 by filling a glass tube with mercury and inverting it into a dish. He noticed the mercury column height changed with weather, proving air has weight and exerts pressure. The unit "torr" honors him. At sea level, mercury rises to about 760mm - this became the standard "atmosphere" of pressure.

Frequently Asked Questions

What's the difference between gauge and absolute pressure?

Gauge pressure measures relative to atmospheric pressure (what most gauges show). Absolute pressure includes atmospheric pressure. To convert: Absolute = Gauge + 1 atm. A tire gauge reading 32 PSI (gauge) is actually 32 + 14.7 = 46.7 PSI absolute.

Why are there so many pressure units?

Historical reasons and practical convenience. PSI works well for Imperial measurements, bar is close to atmospheric pressure, mmHg was natural for mercury barometers, and pascal is the coherent SI unit. Each stuck in its domain - changing would cause confusion and errors.

What pressure unit should I use?

Follow your field's convention: kPa or bar for automotive (tires), PSI for US equipment, mmHg for medical (blood pressure), atm or torr for chemistry, pascals for scientific papers. For international work, SI units (pascals) are preferred.

How does altitude affect atmospheric pressure?

Pressure decreases with altitude. At sea level: 1 atm (101.3 kPa). At 5,000 ft: ~0.83 atm. At 10,000 ft: ~0.69 atm. At Mount Everest summit: ~0.33 atm. This is why airplanes must be pressurized and why cooking times increase at high altitude.

What's a vacuum in pressure terms?

A vacuum is pressure below atmospheric. "Perfect vacuum" = 0 absolute pressure (impossible to achieve). Industrial vacuums are measured in torr or mbar. A "good" vacuum might be 0.001 torr. Outer space has about 10⁻¹⁴ torr - extremely close to perfect vacuum.

How do I convert pressure to force?

Force = Pressure × Area. If you have 100 PSI acting on a 2 square inch piston: Force = 100 psi × 2 in² = 200 pounds of force. This is how hydraulic systems multiply force - small pressure on large area creates big force.

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