What is a Pascal? Pressure Units Explained

Definition: One Newton per Square Meter

The pascal (symbol: Pa) is the SI unit of pressure, defined as one newton of force applied over one square meter of area (1 Pa = 1 N/m²). It is also used to measure stress, tensile strength, and elastic modulus. In practical terms, a single pascal is an extremely small amount of pressure — roughly the force exerted by a dollar bill resting flat on a table. This is why you will almost always see pascals used with metric prefixes: kilopascals (kPa), megapascals (MPa), hectopascals (hPa), or gigapascals (GPa).

Named After Blaise Pascal

The unit honors Blaise Pascal (1623–1662), the French mathematician, physicist, and philosopher who made groundbreaking contributions to the study of fluid mechanics and pressure. Pascal demonstrated that atmospheric pressure decreases with altitude — he famously arranged for his brother-in-law to carry a barometer up the Puy de Dôme mountain in 1648, confirming that the mercury level dropped at higher elevations. His work laid the foundation for hydraulics, pneumatics, and our modern understanding of pressure.

Relationship to Other Pressure Units

The pascal sits at the center of a web of pressure units, each favored by different industries. Here are the key relationships:

• 1 atmosphere (atm) = 101,325 Pa = 101.325 kPa
• 1 bar = 100,000 Pa = 100 kPa (very close to 1 atm)
• 1 PSI (pound per square inch) = 6,894.76 Pa ≈ 6.895 kPa
• 1 mmHg (millimeter of mercury) = 133.322 Pa
• 1 torr ≈ 133.322 Pa (nearly identical to 1 mmHg)

Convert between all of these instantly with our pressure converter.

Why Kilopascals Are More Practical

Because one pascal is so small, everyday applications use scaled-up versions. The kilopascal (kPa)is the most versatile: tire pressure is typically 200–250 kPa (29–36 PSI), standard atmospheric pressure is 101.3 kPa, and blood pressure of 120/80 mmHg equals about 16.0/10.7 kPa. The megapascal (MPa)appears in materials science and structural engineering — the yield strength of mild steel is around 250 MPa. The gigapascal (GPa) measures extreme pressures, such as the modulus of elasticity for metals (steel is roughly 200 GPa).

Where Pascals Are Used in Practice

Weather and Meteorology

Weather services worldwide report atmospheric pressure in hectopascals (hPa), which are numerically identical to millibars (mbar). Standard sea-level pressure is 1013.25 hPa. A deep low-pressure system might read 960 hPa, while a strong high-pressure system could reach 1040 hPa. When a weather report mentions “falling pressure,” it means the hPa reading is decreasing, often signaling incoming storms.

Tire Pressure

In countries using the metric system, tire pressure is specified in kPa. A passenger car typically requires 220–240 kPa (32–35 PSI). Many tire gauges display both units, but if yours only shows kPa, remember that dividing by approximately 6.9 gives you PSI.

Engineering and Materials Science

Engineers use MPa to describe material properties such as tensile strength, compressive strength, and elastic modulus. Concrete compressive strength is commonly specified as 20–40 MPa for residential construction. See our engineering conversions guide for more on pressure and stress unit conversions.

Medicine

While blood pressure is traditionally measured in mmHg, some European medical systems report values in kPa. Converting between them is straightforward: multiply mmHg by 0.1333 to get kPa. Our medical conversions guide covers this and other clinical pressure conversions in detail.

Atmospheric Pressure and Altitude

Atmospheric pressure decreases with altitude because there is less air above you pushing down. At sea level, pressure is 101.325 kPa. At 1,000 meters elevation, it drops to roughly 90 kPa. At the summit of Mount Everest (8,849 m), pressure is only about 33.7 kPa — roughly one-third of sea level. This pressure drop explains why water boils at lower temperatures at altitude and why aircraft cabins must be pressurized.

Pascal's Law and Hydraulic Systems

Pascal's law states that pressure applied to a confined fluid is transmitted equally in all directions throughout the fluid. This principle is the foundation of all hydraulic systems — from car brakes to construction excavators to hydraulic presses. By applying a small force over a small piston area and transmitting that pressure to a larger piston, hydraulic systems multiply force dramatically. A mechanic pressing a brake pedal can generate enough force to stop a two-ton vehicle, all thanks to Pascal's insights from nearly four centuries ago.