Pressure Converter - Pa, kPa, Bar, PSI, atm & Torr

Pressure Converter – Pa, kPa, Bar, PSI, atm & Torr

Pressure: Force Per Unit Area

Pressure measures how much force is applied over a given area. Push a nail with your thumb and the sharp point concentrates all that force into a tiny area — high pressure. Push with your palm and the same force is spread across a much larger area — low pressure. Mathematically: Pressure = Force / Area.

This concept appears everywhere: the air pushing against every surface (atmospheric pressure), gas compressed in a car tire, steam in a boiler, water at depth in the ocean, and blood pumping through arteries. Each context has evolved its own preferred pressure unit, which is why this converter is useful.

The Six Units Supported

Pascal (Pa) is the SI base unit of pressure, defined as one newton of force per square meter of area. Individual Pascals are very small — atmospheric pressure at sea level is about 101,325 Pa. For this reason, kilopascals (kPa) are more practical: 1 kPa = 1,000 Pa. Standard atmosphere = 101.325 kPa.

Bar is a metric unit equal to exactly 100,000 Pa. It's close to but not equal to 1 atmosphere (1 atm = 1.01325 bar). Bar is widely used in European industry, compressors, and hydraulic systems.

PSI (pounds per square inch) is the imperial pressure unit. One psi = 6,894.757 Pa. PSI dominates in the US for tire pressures, hydraulics, plumbing, and compressed gas. A car tire is typically inflated to 30-35 psi.

Atmosphere (atm) is a reference unit equal to exactly 101,325 Pa — defined as the average air pressure at sea level. It's used as a baseline reference in chemistry, diving, and gas law calculations.

Torr (mmHg) equals 133.322 Pa. Historically defined as the pressure of 1 mm of mercury, it remains standard in vacuum science, blood pressure measurements (a normal reading is 120/80 mmHg), and laboratory instruments.

The Default Example Verified

The calculator converts 1 atm to psi by default:

• 1 atm = 101,325 Pa
• 101,325 / 6,894.757293168 = 14.695949 psi

The calculator displays 14.695949 psi. This matches exactly.

A Fourth Worked Example (2 Bar to kPa and PSI)

Industrial compressor and pump gauges are often marked in bar. Converting 2 bar:

1. Convert to Pascals: 2 × 100,000 = 200,000 Pa
2. Convert to kPa: 200,000 / 1,000 = 200 kPa
3. Convert to psi: 200,000 / 6,894.757293168 = 29.008 psi

Verification Result: 2 bar = 200 kPa = 29.008 psi.

Gauge Pressure vs. Absolute Pressure

This is an important distinction that the converter itself does not handle automatically.

Absolute pressure is measured from a perfect vacuum (zero pressure). Gauge pressure is measured relative to atmospheric pressure — a gauge that reads 0 psi when open to air is measuring gauge pressure.

When you inflate a car tire to "35 psi," your gauge is reading gauge pressure. The absolute pressure inside the tire is actually 35 + 14.7 = 49.7 psi absolute (adding 1 atmosphere). In engineering datasheets, pressures are sometimes labeled "psig" (gauge) and "psia" (absolute) to make this explicit.

This converter translates numerical values between pressure units. It does not automatically account for the 1 atm offset between gauge and absolute. If you need to convert gauge pressure in one unit to absolute pressure in another, add 1 atm (or 14.696 psi or 1.01325 bar) first, then convert.

Common Mistakes

Frequently Asked Questions (FAQ)

Q1: What is standard atmospheric pressure in different units?

One standard atmosphere (1 atm) equals exactly 101,325 Pa = 101.325 kPa = 1.01325 bar = 14.6959 psi = 760 Torr. This is the internationally defined reference pressure, approximately equal to the average air pressure at sea level on Earth.

Q2: What is the difference between bar and PSI?

Both are practical pressure units but from different systems. Bar is metric: 1 bar = 100,000 Pa, close to atmospheric pressure. PSI (pounds per square inch) is imperial: 1 psi = 6,894.76 Pa. One bar = 14.5038 psi. European tire pressure gauges use bar; US gauges typically use psi. A tire inflated to 2.5 bar is at 2.5 × 14.5038 = 36.26 psi.

Q3: What is the difference between gauge pressure and absolute pressure?

Absolute pressure is measured relative to a perfect vacuum (zero pressure). Gauge pressure is measured relative to atmospheric pressure, meaning gauge pressure = absolute pressure − 1 atm. Tire pressure gauges read gauge pressure — when a gauge reads 35 psi, the absolute pressure inside the tire is 35 + 14.7 = 49.7 psi absolute. This converter converts numerical values between units but does not automatically adjust between gauge and absolute. If your data is in gauge psi and you need absolute bar, you would need to add 1 atm (14.7 psi) first, then convert.

Q4: What is Torr and why is it used?

Torr (named after Evangelista Torricelli) is a unit of pressure equal to 1/760 of an atmosphere, which works out to 133.322 Pa. Historically it was defined as the pressure exerted by 1 millimeter of mercury (mmHg) at 0°C under standard gravity, which is why Torr and mmHg are treated as equivalent. Torr is common in vacuum science, medical blood pressure (a normal reading is around 120/80 mmHg), and laboratory instruments.

Q5: What is the difference between kPa and Pa?

One kilopascal (kPa) = 1,000 Pascals (Pa). Pa is the SI base unit; kPa is more practical for everyday measurements because individual Pascals are small. Standard atmospheric pressure is 101,325 Pa = 101.325 kPa. Tire pressures are typically in the range 200-300 kPa (200,000-300,000 Pa). Weather forecasters often cite pressure in hPa (hectopascals), where 1 hPa = 100 Pa — a standard day is about 1,013 hPa.