Pressure Converter — Pa, kPa, bar, psi, atm, torr & inHg

A reliable pressure converter is one of those small utilities that turns out to be useful almost every week — whether you're checking a tire gauge that reads in PSI against a spec sheet written in kPa, reading a weather report in inHg, or converting a lab reading between bar and atmospheres for a chemistry assignment. Pressure is deceptively simple in concept (force spread over area) but it is expressed in more competing units than almost any other physical quantity, which is exactly why mistakes happen so often.

This free tool from Arb Digital lets you convert between eight common pressure units — pascal, kilopascal, megapascal, bar, psi, atmosphere, torr (mmHg), and inches of mercury — using exact SI-derived conversion factors, not rounded approximations. Type a number, pick your source and target unit, and every result updates immediately in your browser.

What This Pressure Converter Does

The tool takes a single input value and a "from" unit, converts it internally to the SI base unit for pressure (the pascal), and then converts that pascal figure into whatever "to" unit you select. Because every unit routes through one common base rather than being converted directly from unit to unit, the math stays exact regardless of which combination you pick — there's no compounding rounding error from chained approximations. Alongside the headline conversion, the tool also shows your value simultaneously in PSI, bar, atmospheres, and kilopascals, since those four units cover the vast majority of everyday and professional use cases: tire pressure, cooking (pressure canners), scuba and diving tables, weather reports, and industrial or scientific specifications.

How to Use the Pressure Converter

1. Enter your value. Type the number you want to convert into the amount field — for example, 32 for a typical car tire reading.
2. Choose the "From" unit. Select the unit your original number is expressed in, such as PSI.
3. Choose the "To" unit. Pick the unit you need the answer in, such as kilopascals or bar.
4. Read the result. The converted figure appears instantly in the result panel, along with the same value expressed in four other common pressure units.
5. Use the swap button to flip the "from" and "to" units in one click if you need to reverse the conversion.

The Formula Behind Every Pressure Conversion

Pressure is defined physically as force per unit area (P = F ÷ A), and the SI unit — the pascal (Pa) — equals one newton of force per square meter. Every other pressure unit in this tool is defined as a fixed multiple of the pascal, so converting between any two units is a two-step process: multiply your input by its unit's pascal-equivalent to get pascals, then divide by the target unit's pascal-equivalent. The National Institute of Standards and Technology publishes the authoritative conversion factors used here in its Guide for the Use of the International System of Units (NIST SP811): 1 psi = 6,894.757293168 Pa, 1 atmosphere = exactly 101,325 Pa, 1 bar = exactly 100,000 Pa, and 1 torr = 101,325 ⁄ 760 Pa (≈133.322 Pa). Because the tool always routes through pascals as the common base, converting straight from torr to psi, for instance, is exactly as accurate as converting from pascal to kilopascal — there is no accuracy penalty for choosing an "unusual" pair of units.

Tire Pressure: Why PSI, Bar, and kPa All Matter

Tire pressure is probably the single most common real-world reason people search for a pressure converter. In the United States, tire placards and gauges almost always read in PSI, while vehicles manufactured for European or Asian markets frequently list recommended pressures in bar or kPa on the door jamb sticker. A typical passenger car tire runs somewhere between 30 and 36 PSI (about 2.1 to 2.5 bar, or 207 to 248 kPa), while many bicycle tires run dramatically higher — a narrow road bike tire might call for 90 to 120 PSI (roughly 6.2 to 8.3 bar). Getting the unit wrong isn't a rounding error; mistaking bar for PSI, for example, would mean inflating a tire to nearly 14.5 times the intended pressure, which is dangerous. Whenever a spec sheet, an imported vehicle manual, or an online forum quotes a pressure in an unfamiliar unit, running it through this converter before you pick up the air hose is the safest habit.

Weather and Barometric Pressure

Meteorologists and aviation weather reports commonly use inches of mercury (inHg) in the United States, hectopascals (hPa, numerically identical to millibars and equal to 0.1 kPa) almost everywhere else, and occasionally millimeters of mercury for altimeter settings. Standard sea-level atmospheric pressure is defined as exactly 1 atmosphere, which equals 29.92 inHg, 1,013.25 hPa, or 14.696 PSI. The National Oceanic and Atmospheric Administration explains how these readings drive forecasting and altimeter calibration in its public JetStream guide to atmospheric pressure. If you've ever wondered why a "high pressure system" described as 30.24 inHg on a US radio broadcast is reported as roughly 1,024 hPa on an international weather app, this converter closes that gap in a single step.

Industrial, Scientific, and Medical Uses

Engineers and scientists lean on pascal, kilopascal, megapascal, and bar far more than psi, since these are the units baked into SI-based equations for stress, hydraulics, and gas laws. Medical devices such as blood pressure cuffs traditionally read in mmHg (essentially identical to torr), pressure canners and autoclaves are often rated in PSI, and hydraulic systems in heavy machinery are commonly specified in bar or MPa. Because so many industries default to different conventions, a chemistry student converting a gas-law problem, a machinist reading a hydraulic press spec, or a home cook following a pressure-canning recipe from an international source will all reach for slightly different units — and all can use the same converter to move between them without manual arithmetic.

• Cooking & canning: pressure canners typically operate around 10–15 PSI (0.69–1.03 bar) above atmospheric pressure.
• Scuba diving: tank pressures are often rated in bar (200–300 bar) or PSI (3,000–4,500 PSI) depending on the manufacturer's home market.
• HVAC & refrigeration: refrigerant gauges commonly mix PSI and bar readings on the same manifold.
• Structural engineering: material stress and strength are usually expressed in MPa or PSI in engineering datasheets.

Gauge Pressure, Absolute Pressure, and Vacuum Readings

One nuance this converter deliberately leaves to the user is the distinction between gauge pressure and absolute pressure. Gauge pressure is measured relative to the surrounding atmosphere and reads zero at ambient conditions — this is how virtually every tire gauge, blood pressure cuff, and shop air compressor gauge works. Absolute pressure, by contrast, is measured relative to a perfect vacuum, so it always includes the roughly 14.7 PSI of atmospheric pressure pressing down on us at sea level. A "0 PSI" gauge reading is actually about 14.7 PSI absolute. Vacuum gauges add a third wrinkle, since they typically read the shortfall below atmospheric pressure rather than the pressure itself — a reading of "10 inHg vacuum" means the pressure inside a system is 10 inHg below the surrounding atmosphere, not 10 inHg in absolute terms. Whenever you convert a pressure value with this tool, it's worth pausing to confirm whether the source figure is gauge, absolute, or vacuum, since the unit conversion itself is identical in all three cases but the practical meaning is not.

This distinction matters most in fields like HVAC refrigerant charging, vacuum pump specifications, and industrial process control, where absolute and gauge readings are used side by side and a mismatch can lead to a system being charged incorrectly or a safety threshold being misjudged. Aviation altimetry adds yet another layer: pilots set their altimeters using a "QNH" or "QFE" barometric reference, both of which are pressure values expressed in inHg or hPa, but calibrated to different reference points (sea level vs. field elevation). None of these context-specific adjustments change the underlying unit-conversion math this tool performs — they simply determine which starting number you should be converting in the first place.

Common Mistakes to Avoid

• Confusing gauge pressure with absolute pressure. Tire gauges and most consumer pressure readings are "gauge" pressure — they already exclude the surrounding atmosphere. This converter performs unit conversion only; it does not add or remove atmospheric baseline pressure.
• Mixing up bar and PSI. These units differ by a factor of roughly 14.5 — an easy typo to make when copying specs manually.
• Assuming 1 mmHg equals 1 torr in every historical context. They are extremely close (within 0.000015%) and treated as identical for virtually all practical purposes, which is what this tool does.
• Rounding too early. Converting through a rounded intermediate value (e.g., "1 atm ≈ 1 bar") introduces small but avoidable errors — this tool always uses the full-precision NIST-published factors.

Related Free Tools From Arb Digital

If pressure units aren't the only thing you need to convert today, try our Energy Converter for joules, calories, and kWh, our Power Converter for watts and horsepower, or our Force Converter for newtons and pound-force. For everyday measurements, check out the Length Converter and Weight Converter as well. You can browse everything we offer on our free online tools hub.

Frequently Asked Questions