Free Pressure Converter Online

A pressure converter takes a reading in one pressure unit — pascals from an SI formula, psi from a tire gauge, atmospheres from a chemistry problem, mmHg from a barometer or a blood-pressure cuff — and returns the exact equivalent in the other units used to describe the same physical quantity: force distributed over an area. This one covers seven units — pascals (Pa), kilopascals (kPa), bar, psi, atmospheres (atm), millimeters of mercury (mmHg), and torr — using exact definitional factors, including a genuinely tiny but real difference between mmHg and torr that most quick-reference charts quietly ignore.

How the Pressure Converter Works

Type a pressure value into the single input box — the tool assumes bar, the unit most tire gauges and weather reports outside the US default to — and the output panel fills in automatically, typically inside a third of a second after you stop typing, restating that same pressure in pascals, kilopascals, psi, atmospheres, and mmHg. Real-time auto-convert is switched on out of the box; a small toggle swaps it for a manual button instead, in case you'd rather finish entering a decimal value before the recalculation fires. A Copy control puts the whole result block on your clipboard, a Save button writes it out as a text file, and a Clear button resets both panes for the next reading. Nothing about the interface requires signing up first. Developers who need the same bar-to-everything math inside a script or app can call the metered API version described at /docs instead of re-implementing the seven-unit formulas from scratch.

As a worked example: typing 2 into the field — 2 bar — returns 200,000 Pa, 200 kPa, about 29.01 psi, roughly 1.9738 atm, and approximately 1,500.12 mmHg, every figure computed from the exact factors in the table further down rather than a rounded shortcut.

Why People Convert Pressure Units

Pressure gets measured differently depending on the instrument, the country, and the field, which is exactly when a mismatch tends to surface:

• Checking tire pressure. US gauges read psi, while most of the rest of the world reads bar or kPa, so a rental car abroad or an imported vehicle's door-jamb sticker often needs converting before you can trust the number on your own gauge. A US-spec 32 psi recommendation, for instance, converts to about 2.206 bar or 220.6 kPa on a European tire-pressure placard.
• Cross-checking weather readings. International forecasts frequently quote barometric pressure in kPa, while a home weather station or an older barometer might be calibrated in mmHg instead. A forecast reading of 101.3 kPa, for example, sits at almost exactly 1.013 bar, just a hair above the standard atmosphere baseline of 101.325 kPa.
• Reading blood pressure figures. Blood pressure is conventionally recorded in mmHg — that's literally what the "120" in a "120/80" reading means — and some lab equipment or research papers report the same measurement in kPa or Pa instead. A "120 over 80" reading, for instance, corresponds to roughly 16.0 kPa over 10.7 kPa on an instrument calibrated in SI units.
• Gas-law coursework. Chemistry and physics problems built around PV = nRT mix atm, kPa, and Pa depending on where the textbook was written, and getting the units consistent is half the battle in solving the equation correctly. A problem stated in 2.5 atm, for example, needs restating as 253,312.5 Pa before it can go into a formula written entirely in SI units.
• Comparing industrial or HVAC equipment. A US-market gauge or compressor is rated in psi, while the same category of equipment from a European manufacturer publishes its rating in bar. A compressor rated at 150 psi, for example, corresponds to roughly 10.34 bar on a European nameplate.

Understanding How Each Pressure Unit Is Defined

Unit	Symbol	Exact value in pascals
Pascal	Pa	1 — the SI base unit: one newton of force per square meter
Kilopascal	kPa	1,000 Pa
Bar	bar	100,000 Pa — a round-number unit popular in meteorology and industry, close to but not identical to one atmosphere
Pound per square inch	psi	6,894.75729 Pa — one pound-force acting over one square inch
Standard atmosphere	atm	101,325 Pa — the defined standard for atmospheric pressure at sea level
Millimeter of mercury	mmHg	133.322387 Pa — the pressure exerted by a 1 mm column of mercury under standard gravity and density conditions
Torr	torr	133.322368 Pa — defined as exactly 1/760 of a standard atmosphere

mmHg and torr look identical at a glance, and for nearly every practical purpose they are — the two units were designed to be interchangeable, and they still agree to five significant figures. But they aren't defined the same way. The millimeter of mercury is a physical definition: the pressure exerted by a column of mercury exactly 1 millimeter tall, worked out from a conventional mercury density and standard gravity. The torr, introduced later, is a purely numerical definition instead: exactly 1/760 of a standard atmosphere, or 101,325 ÷ 760 = 133.322368421... pascals. Because mercury's physical properties don't happen to divide the atmosphere into a round number, the physically-defined mmHg (133.322387 Pa) and the arithmetically-defined torr (133.322368 Pa) diverge in the sixth significant figure — a gap far below what any analog gauge could register, but not literally zero. This converter keeps the two as separate units specifically so that distinction stays visible instead of getting rounded away.

Approach	Tradeoff
Standardizing on Pa or kPa	Matches SI and every physics formula directly, but everyday pressures like a car tire become five- or six-digit numbers
Using bar or atm for rough intuition	Both sit close to typical atmospheric and tire pressures, so the numbers stay small and memorable, but neither is the base SI unit, so formulas still need a conversion step first
Using psi for US equipment specs	Matches how US tire, plumbing, and pneumatic-tool gauges are labeled, but doesn't translate to a metric spec sheet without converting first
Using mmHg for medical readings	Matches the convention doctors and nurses actually read blood pressure and manometers in, but is easy to confuse with the near-identical torr used in vacuum and lab equipment

Whichever unit you settle on for everyday reading, the tool itself always computes through the exact pascal-based factors in the table above, so the choice of display unit is purely a matter of convenience and never trades away precision — the mmHg-versus-torr distinction included.

Pressure Converter vs. Manual Conversion Methods

• Working it out by hand. Converting psi to Pa alone means multiplying by a seven-digit factor (6,894.75729), and doing that correctly across five or six units at once invites an arithmetic slip — a single misplaced decimal in a bar-to-psi conversion can be the difference between an over-inflated tire and a properly filled one.
• A scientific calculator's unit mode. It works, but pressure is usually buried a few menus deep, and it converts one pair of units at a time rather than showing every unit at once, so checking a value against five different units means running the same conversion five separate times.
• A gas-law textbook's conversion table. Fine for a single lookup, but static — it gives you a factor to apply by hand, not an instant, checked answer for an arbitrary decimal reading, and most printed tables stop at atm, Pa, and mmHg without covering bar, psi, or torr at all.
• This tool. One field, every common pressure unit at once, and the exact torr-versus-mmHg distinction preserved rather than collapsed into a single rounded figure, with the identical math available through the API for anyone converting more than a handful of readings.

How Your Readings Are Handled

The conversion runs locally, inside your browser, the moment you stop typing — the pressure value you enter is never sent off to a server to generate the multi-unit result, so there's nothing transmitted for anyone to intercept. No account, login, or installed software is involved, and the figure you typed isn't retained anywhere once you leave the page.

Common Questions About Converting Pressure Units

Why do mmHg and torr give slightly different numbers for the same pressure?

mmHg is defined from the physical properties of mercury under standard gravity, while torr is defined as an exact fraction of one standard atmosphere — the two agree to about five significant figures but aren't mathematically identical, which is why this tool tracks them as separate units.

What's standard atmospheric pressure in each of these units?

One standard atmosphere is, by definition, 101,325 Pa, which works out to 101.325 kPa, 1.01325 bar, roughly 14.6959 psi, and 760 mmHg — and, since torr is defined as exactly atm ÷ 760, also precisely 760 torr, one of the few places where the tiny mmHg-versus-torr gap is visible even before any rounding.

Is a bar the same thing as one atmosphere?

Close, but not identical — 1 bar equals 100,000 Pa, while 1 standard atmosphere equals 101,325 Pa, so a bar reads about 1.3% lower than a true atmosphere. The two get treated as interchangeable in casual conversation because they're so close, but a precise calculation should use whichever one the source actually specifies.

My tire's sidewall lists a maximum in psi but my gauge reads bar — which number do I use?

Convert one to the other rather than guessing — 1 psi equals 6,894.75729 Pa, so a psi figure translates to bar by multiplying by that factor and dividing by 100,000, or you can just run the number through this tool directly. Tire pressure is one of the more common places drivers run into a mismatch between a US-labeled sidewall and a metric-only gauge.

Why is blood pressure measured in mmHg instead of a more common unit like kPa?

Convention and history — early blood pressure measurement used actual mercury-column manometers, and the mmHg reading it produced stuck as the medical standard even after most instruments moved to digital and electronic sensors. Some countries and some lab contexts do report blood pressure in kPa, which is exactly the conversion this tool performs.

A weather app shows pressure in hPa — how does that relate to the units here?

A hectopascal (hPa) is exactly 100 pascals, and it's numerically identical to a millibar, a unit meteorology used for decades before hPa became the standard label. Since this tool's kPa unit is 1,000 pascals, 1 kPa always equals 10 hPa — so a forecast reading of 1,013 hPa converts to 101.3 kPa here, close to the standard-atmosphere value of 101.325 kPa.

Related Tools

Pressure and temperature are linked directly through the gas laws, so anyone converting a chemistry problem's units will likely also need the Temperature Converter to fully restate a PV = nRT scenario in consistent units. Pressure gauges are frequently paired with linear measurements — tank depth, pipe diameter, altitude — which the Length Converter handles. Weather and diving contexts often mix pressure readings with wind or descent speed, covered by the Speed Converter, and since pressure is technically force distributed over area, the Weight Converter — for the mass and force side of that relationship — rounds out the set.