Pressure Converter

Pressure Converter — Convert Between All Pressure Units Online

The Pressure Converter by Toolsiro converts between 11 pressure units instantly — Pascal, Kilopascal, Megapascal, Bar, Millibar, PSI, Atmosphere, Torr, mmHg, inHg, and Hectopascal. Type a value, select your unit, and all conversions update in real time. Click any result card to use that value as your new input.

Pressure measurements appear across nearly every field of science and engineering. Weather forecasts report atmospheric pressure in millibars or hectopascals. Tire gauges read in PSI. Medical equipment uses mmHg for blood pressure. Industrial systems work in bar or PSI. Physics and chemistry use Pascals as the SI unit. This tool brings all these units together in one place.

Understanding the Pascal — The SI Unit of Pressure

The Pascal (Pa) is the International System of Units (SI) base unit of pressure, defined as one Newton of force per square meter (N/m²). Named after the French mathematician and physicist Blaise Pascal, it is the scientific standard for pressure measurement worldwide. Because atmospheric pressure is approximately 101,325 Pa, the kilopascal (kPa) and megapascal (MPa) are more practical for everyday use — 1 atm equals 101.325 kPa or 0.101325 MPa.

The hectopascal (hPa), equal to exactly 100 Pa, is numerically identical to the millibar and is the preferred unit in meteorology worldwide. Weather stations, barometers, and weather apps universally report pressure in hPa because it gives convenient numbers for atmospheric pressure — standard atmosphere is 1013.25 hPa.

Bar and Millibar — Industrial and Meteorological Standards

The bar is widely used in industry, engineering, and scientific contexts outside the United States. It equals exactly 100,000 Pa (100 kPa), making it very close to but not exactly equal to one standard atmosphere (1 atm = 1.01325 bar). Tire pressure gauges in many countries read in bar. Scuba diving depth calculations, pneumatic systems, hydraulic machinery, and compressed gas specifications commonly use bar or millibar.

The millibar (mbar) equals 0.001 bar or 100 Pa. Standard atmospheric pressure is 1013.25 mbar. Millibar was the primary meteorological unit for decades before hectopascal became the official SI-preferred alternative — they are numerically identical, so 1013.25 mbar equals 1013.25 hPa exactly.

PSI — The Everyday Pressure Unit in the US

PSI (pounds per square inch) is the pressure unit most familiar to Americans, appearing on tire pressure gauges, bicycle pumps, air compressors, blood pressure monitors (alongside mmHg), and most industrial gauges used in the United States. One PSI equals approximately 6,894.76 Pa or about 0.0689 bar.

Standard atmospheric pressure at sea level is approximately 14.696 PSI. Car tire pressure typically ranges from 30 to 35 PSI. Bicycle tires range from 80 to 130 PSI for road bikes. Hydraulic systems can operate at thousands of PSI. Industrial high-pressure applications may reach tens of thousands of PSI.

Atmosphere (atm) — The Natural Reference Point

One standard atmosphere (atm) is defined as exactly 101,325 Pa. It was originally defined as the average atmospheric pressure at sea level, providing a natural reference point that humans have used for centuries. Despite not being an SI unit, atm remains widely used in chemistry (for gas law calculations), diving (to describe water pressure at depth), and as a convenient reference in scientific contexts.

Water pressure increases by approximately 1 atm for every 10 meters of depth, making atm a natural unit for scuba diving. At 10 meters, total pressure is 2 atm; at 30 meters, it's 4 atm. This relationship also explains why the bends (decompression sickness) risk increases sharply with depth.

Torr and mmHg — Medical and Vacuum Measurement

Torr (named after Evangelista Torricelli, inventor of the barometer) and millimeters of mercury (mmHg) are effectively the same unit — 1 Torr is defined as 1/760 of a standard atmosphere, which is approximately 133.322 Pa. The slight technical difference between Torr and mmHg is negligible for most practical purposes.

Blood pressure is universally reported in mmHg. A normal reading of 120/80 mmHg means a systolic pressure of 120 mmHg and diastolic pressure of 80 mmHg. Vacuum systems are also measured in Torr — a rough vacuum might be at 1 Torr, while a high vacuum system achieves 10⁻³ Torr or lower. Inches of mercury (inHg) is used in aviation and some weather reporting in the United States.

Pressure in Everyday Life

Pressure measurements affect daily life in many ways that often go unnoticed. The atmospheric pressure at your location determines weather patterns and affects how your body feels — dropping pressure typically signals incoming storms while rising pressure indicates clearing weather. Cabin pressure in commercial aircraft is maintained at the equivalent of approximately 6,000 to 8,000 feet altitude (about 75–80 kPa) rather than the ambient pressure at cruising altitude (about 20–25 kPa), making pressurization essential for passenger comfort and safety.

Blood pressure, measured in mmHg, is one of the most important indicators of cardiovascular health. Tire pressure in PSI directly affects fuel economy, handling, and tire longevity. Cooking at altitude requires adjusted recipes because water boils at lower temperatures when atmospheric pressure is lower — at 5,000 feet, water boils at about 95°C instead of 100°C.

Common Pressure Conversions Reference

1 standard atmosphere (atm) = 101,325 Pa = 101.325 kPa = 1.01325 bar = 1013.25 mbar = 1013.25 hPa = 14.696 PSI = 760 Torr = 760 mmHg = 29.92 inHg. These conversions appear constantly in scientific literature, engineering tables, and technical documentation — bookmarking this page gives you instant access to all of them without memorization.

Gauge Pressure vs Absolute Pressure

An important distinction in pressure measurement is between absolute pressure and gauge pressure. Absolute pressure measures pressure relative to a perfect vacuum (zero pressure). Gauge pressure measures pressure relative to current atmospheric pressure. A car tire inflated to 32 PSI gauge pressure contains air at approximately 32 + 14.7 = 46.7 PSI absolute. Most everyday pressure gauges read gauge pressure, which is why they read zero when the tire is flat (ambient pressure) rather than 14.7 PSI. This tool converts absolute pressure values — be aware of which type you're working with when applying conversions to real-world measurements.

Frequently Asked Questions

What is standard atmospheric pressure in different units? 101,325 Pa = 101.325 kPa = 1.01325 bar = 1013.25 mbar = 14.696 PSI = 1 atm = 760 mmHg = 760 Torr = 29.921 inHg = 1013.25 hPa.

What pressure unit does weather use? Meteorology uses hectopascals (hPa) internationally, which are numerically identical to millibars (mbar). The United States also uses inches of mercury (inHg) in some weather reporting contexts.

Why does blood pressure use mmHg? Mercury manometers were the original instruments for measuring blood pressure, and the unit persisted because of medical tradition even after electronic sensors replaced mercury devices. The values are now so deeply embedded in clinical practice and reference ranges that changing units would create dangerous confusion.

What's the difference between PSI and PSIA? PSI typically refers to gauge pressure (relative to atmosphere). PSIA (PSI Absolute) is explicitly absolute pressure. PSIG (PSI Gauge) makes the distinction explicit. This tool works with absolute values.

High-Pressure and Low-Pressure Applications

Pressure ranges vary enormously across different fields. Atmospheric pressure at sea level is about 101.3 kPa. Deep sea at the Mariana Trench reaches approximately 110 MPa (about 1,086 atm). Hydraulic systems in heavy machinery operate at 10–35 MPa. Autoclaves for sterilization run at around 200 kPa. Diamond anvil cells used in research can generate over 300 GPa — three million times atmospheric pressure. On the low end, a typical household vacuum cleaner creates a pressure difference of about 20–25 kPa below atmospheric. Scientific vacuum chambers achieve pressures below 10⁻¹⁰ Pa. Understanding which unit is appropriate for your pressure range helps avoid awkward numbers with many zeros.

For most everyday applications, kPa and PSI cover the practical range of pressures people encounter. For scientific work, SI units (Pa, kPa, MPa) are standard. For weather, hPa and mbar. For medical, mmHg. For industrial Europe, bar. The unit converter handles all of these seamlessly.