Convert between psi, bar, atm, kPa, MPa, mmHg and more — with the full conversion steps shown.
Every tire you inflate, every weather report you read, every scuba gauge you glance at is a pressure number — force spread over an area — and each industry quotes it in different units. Meteorologists speak hectopascals, tire shops speak psi, engineers speak bar, and scientists speak atmospheres, and mixing them up means a “correct” calculation that quietly fails. Our free Pressure Converter converts any supported pressure unit to any other and shows the two-step working — input to the pascal base, then to the target — so every digit is verifiable.
Pressure is defined simply as force divided by area: P = F/A. Its SI unit, the pascal, is one newton per square meter — a tiny unit, so real-world pressures are usually quoted in kilopascals, bars, or atmospheres. The variety is historic: the millimeter of mercury goes back to Torricelli’s 1643 barometer, the atmosphere is the average pressure at sea level, and psi is the everyday unit of the US and UK mechanical world. Each is exact by definition now: 1 atm = 101325 Pa, 1 bar = 100000 Pa, 1 psi = 6894.757293 Pa.
Enter any value, choose the source and target units, and the converter returns the result to four decimals plus a bonus: the ratio to one standard atmosphere, with a plain-English verdict — pressurized, partial vacuum, or exactly atmospheric. Whether you are a student checking a physics problem, a diver planning gas, or an engineer sizing a vessel, the steps are transparent and the math is exact.
Pressure is force per unit area: P = F/A. Push a 10-newton force through a 2-square-meter plate and you get 5 pascals. Because the pascal is small — the pressure of a dollar bill lying flat — practical work uses larger units: the bar (100000 Pa, roughly one atmosphere), the psi (pound-force per square inch, 6894.76 Pa), and the standard atmosphere (101325 Pa, the agreed average at sea level).
Absolute vs. gauge: most gauges read gauge pressure — pressure above the surrounding atmosphere — while physics calculations use absolute pressure, measured from a perfect vacuum. A tire at 32 psi gauge holds about 46.7 psi absolute. The converter assumes absolute values on both sides, so add or subtract 1 atm when bridging between a gauge reading and an absolute one.
The classic units: the mmHg (torr) is the pressure that supports a 1 mm column of mercury — 133.322 Pa — still used in medicine (blood pressure) and vacuum work. The hectopascal (100 Pa) equals the old millibar of weather maps; a 1013 hPa high-pressure system is 1.013 bar. None of these are mysterious: each is an exact multiple of the pascal.
Key terms:
Every conversion passes through the SI base pascal, exactly as the widget’s step line shows. The bar’s clean 100000 factor is why engineers prefer it over atmospheres in calculations — one fewer awkward decimal.
A car tire is inflated to 32 psi gauge. Express that in bar.
European tire placards quote ~2.2 bar for passenger cars — the converter reproduces the placard value, confirming the gauge is in the right range.
A meteorologist reports a deep low of 980 hPa. How many atmospheres is that?
The 3.3% deficit below one atmosphere is what drives the storm’s winds — pressure gradients, not absolute values, move air.
Jonah tops up his SUV tires before a road trip. The door placard says 35 psi; his European gauge reads in bar. He types 35 psi into the converter and gets 2.4132 bar (35 × 6894.757293 ÷ 100000). The gauge needle sits at 2.4 — within a needle-width of correct, and the converter’s “2.38× atmospheric” note reassures him the reading is sane, not a faulty gauge stuck at zero.
A second scenario: a home brewer force-carbonates a keg at 12 psi gauge. His CO2 chart wants bar: 12 × 6894.757293 ÷ 100000 = 0.8274 bar gauge. He adds one atmosphere to get absolute (1.84 bar absolute) before consulting the carbonation table — the converter handled the units, and his gauge/absolute awareness handled the physics.
A third: a student reads that a scuba tank is filled to 3000 psi and wonders what that means in atmospheres. 3000 × 6894.757293 ÷ 101325 = 204.14 atm — two hundred times the air pressing on your shoulders right now. That number makes the tank’s thick steel suddenly intuitive.
A fourth: a nurse sees a blood pressure of 120/80 mmHg and the converter says 120 mmHg = 15.999 kPa — the physiological pressure that inflates every arterial wall, about 16% of atmospheric pressure. Same physics, gentler scale.
Weather is applied pressure physics: air flows from high to low pressure, and the isobars on a forecast map are contour lines of constant pressure in hectopascals. A 4 hPa difference across 100 km drives a stiff breeze; hurricane hunters fly into eyes near 900 hPa — 11% below normal — where the converter’s atmosphere-ratio readout turns a chart number into visceral understanding.
Diving adds roughly 1 atm per 10 m of seawater. At 30 m a diver breathes air at 4 atm absolute, and nitrogen dissolves into tissues under that pressure — the entire science of decompression tables is pressure bookkeeping. Dive computers think in bar; US training still teaches psi; the converter is the bilingual dictionary.
Aviation altimeters are barometers in disguise: they convert ambient pressure to altitude using the standard atmosphere model. Pilots set the altimeter to local sea-level pressure (QNH, in hPa or inHg) so the dial reads true altitude. A 1 hPa setting error is ~28 ft of altitude error — unit fluency is safety-critical.
Medicine quotes blood pressure in mmHg, ventilators in cmH2O, and vacuum suction in mmHg below atmosphere — three dialects on one ward. The converter’s pascal-base method handles all of them, because every unit is an exact multiple of the pascal.
Industrial process control runs on 4–20 mA loops tied to pressure transmitters calibrated in bar, psi, or kPa depending on the vendor’s home country. Commissioning engineers convert setpoints constantly; a mis-set high-pressure interlock is a burst-disk event, so the two-step shown working is not academic — it is the audit trail.
Vacuum technology spans twelve orders of magnitude, from rough vacuum (mbar) to ultra-high vacuum (10−9 Pa) in chip fabs. Each decade needs different gauges and different units; the converter covers the everyday end of that range, where mbar, torr, and psi overlap and confuse.
Cooking is pressure physics too: a pressure cooker at 15 psi gauge (~2 atm absolute) raises water’s boiling point to 121°C, cooking beans in a third of the time. High-altitude bakers fight the opposite — 0.8 atm in Denver lowers boiling to ~94°C. Same converter, tastier results.
One pattern worth internalizing: quote safety-critical pressures with the unit your audience’s instruments speak. The converter makes translation trivial, but the human step — labeling gauge vs. absolute, US vs. imperial gallon-style traps — is where errors actually happen. Always write the unit, every time.
Pressure converter: input value × (from-factor / to-factor), factors in pascals: atm=101325, bar=100000, psi=6894.757293, mmHg=133.322387, kPa=1000, MPa=1000000, Pa=1. Ratio to 1 atm shown; >1 pressurized, <1 partial vacuum. Source: Sigma Calculator, Pressure Converter, https://sigmacalculator.net/math-calculators/pressure-converter/
Cite this page as: Pressure Converter, Sigma Calculator, https://sigmacalculator.net/math-calculators/pressure-converter/
Last updated: October 12, 2026