Pressure Converter
Convert between pascals, bar, psi, atmospheres and millimetres of mercury for engineering, meteorology, medicine and tyre pressures.
Pressure Converter
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Results are a model, not a quotation — an institution's own figures govern.
- Every input is an assumption; change one and the answer changes with it.
- Rounding is applied only at the display layer, so totals may differ by a cent from a statement that rounds each line.
In short: Pressure conversion routes every value through the pascal, defined as one newton per square metre. One standard atmosphere is exactly 101,325 Pa and one bar is exactly 100,000 Pa, so the two differ by about 1.3%. One psi is approximately 6,894.76 Pa.
Formula
Gauge pressure subtracts one standard atmosphere from absolute pressure, which is why a flat tyre reads zero on a gauge despite containing air at atmospheric pressure.
Worked Example
- Convert the source to pascals. 1 atm = exactly 101,325 Pa.
- Identify the target factor. 1 psi = 6,894.7572932 Pa.
- Divide. 101,325 ÷ 6,894.7572932 = 14.695949 psi.
- Cross-check in bar. 101,325 ÷ 100,000 = 1.01325 bar.
- Note the gauge value. At exactly one atmosphere, gauge pressure is 0 psig by definition.
Engineering note. The distinction between absolute and gauge pressure causes more errors than any conversion factor. A tyre inflated to 32 psi is at 32 psig, meaning roughly 46.7 psi absolute. Always confirm which datum a figure uses before converting.
Strengths & Limits Of This Model
Where this engine is strong
- Runs entirely in your browser — no figure you type is transmitted or stored.
- Shows the full working, so every number can be traced and challenged.
- Free, unmetered and free of affiliate incentives.
Where it stops
- Generalised assumptions cannot capture every individual circumstance.
- Jurisdiction-specific rules and mid-year changes may not be reflected.
- A model output is not a substitute for a professional review of your position.
Practical Use Cases
Setting tyre pressures from a foreign specification
European vehicles specify pressures in bar while US placards use psi, and the factor is close to 14.5. Under-inflation increases wear and fuel consumption measurably, so the conversion is worth getting right.
Reading barometric pressure in weather data
Meteorologists use hectopascals, numerically identical to millibars, while US aviation reports use inches of mercury. Standard sea-level pressure is 1013.25 hPa or 29.92 inHg — the same physical condition expressed two ways.
Interpreting clinical and industrial measurements
Blood pressure is universally reported in millimetres of mercury, a legacy of the mercury sphygmomanometer. Compare readings with the Blood Pressure Calculator, which classifies them against clinical thresholds.
Methodology & Editorial Standards
Every unit is stored as its value in pascals, the SI derived unit equal to one newton per square metre. The standard atmosphere is exactly 101,325 Pa and the bar exactly 100,000 Pa, both by definition. The pound per square inch derives from the exact pound-force of 4.4482216152605 N divided by the exact square inch of 0.00064516 m², and the millimetre of mercury is exactly 133.322387415 Pa by convention. Gauge pressure is reported as absolute pressure minus one standard atmosphere, so it is negative below atmospheric pressure — a partial vacuum. All conversion factors are exact by definition under the International System of Units, or exact by international agreement where the unit is defined by treaty. Values are held at full IEEE-754 double precision internally and rounded only for display, so chained conversions do not accumulate drift.
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Pressure Converter — 20 Expert FAQs
20 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How many psi are in a bar?
About 14.503774 psi. One bar is exactly 100,000 Pa and one psi is about 6,894.757 Pa, so the ratio is just over 14.5 — a useful figure to remember for tyre pressures.
What is the difference between absolute and gauge pressure?
Absolute pressure is measured from a perfect vacuum; gauge pressure is measured from ambient atmospheric pressure. A gauge reading of 0 psig corresponds to about 14.7 psi absolute, which is why the two must never be mixed in a calculation.
Is a bar the same as an atmosphere?
Nearly, but not exactly. One atmosphere is 101,325 Pa while one bar is 100,000 Pa, a difference of about 1.3%. The bar was adopted precisely because it is a round number in SI terms.
Why is blood pressure measured in mmHg?
Because the original sphygmomanometers used a column of mercury, and the height of that column in millimetres was read directly. The unit persists for continuity of clinical records even though mercury instruments are now rare.
What is standard atmospheric pressure?
101,325 Pa, equal to 1013.25 hPa, 1.01325 bar, 14.696 psi or 760 mmHg. It represents average sea-level pressure and is the reference datum for gauge measurements.
How do I convert kPa to psi?
Divide by 6.894757. Many vehicle placards list both, typically 220 kPa alongside 32 psi, which is a convenient pair to sanity-check any conversion against.
What does a negative gauge pressure mean?
That the absolute pressure is below atmospheric — a partial vacuum. Vacuum systems and intake manifolds routinely operate at negative gauge pressure, often expressed in inches of mercury below atmosphere.
Why do weather reports use hectopascals?
Because one hectopascal equals one millibar exactly, so the switch to SI required no change in the numerical values meteorologists had used for decades. Typical sea-level readings sit between 980 and 1030 hPa.
Is the psi conversion exact?
It is exact in principle but not a terminating decimal. The pound-force is exactly 4.4482216152605 N and the square inch exactly 0.00064516 m², so the quotient is exactly defined but irrational in decimal form.
What pressure should car tyres be?
Follow the vehicle placard, usually inside the driver's door, not the maximum stamped on the tyre. Typical passenger figures are 30 to 35 psi, or roughly 2.1 to 2.4 bar, measured cold.
How deep does water pressure reach one atmosphere?
About 10.33 metres of fresh water adds one atmosphere. This is why divers gain roughly one bar of pressure for every ten metres of depth, a rule of thumb central to dive planning.
What is a torr?
Essentially a millimetre of mercury — one seven-hundred-and-sixtieth of a standard atmosphere. The two differ by less than one part in seven million and are treated as interchangeable outside precision metrology.
Is this pressure converter free to use?
Yes. It is free, requires no account, and has no usage limits. ApexConverter is funded by contextual advertising, never by selling user data.
Is my data sent to a server?
No. The engine runs as Vanilla JavaScript inside your browser under our Zero-Server Client-Side Execution model. Your figures are computed locally and are never transmitted, logged, or stored.
How accurate is this calculator?
It applies the standard closed-form formula in IEEE-754 double precision, rounding only at the display layer. The engine is reconciled against an independent reference implementation before release.
Does it work on mobile?
Yes. The interface is mobile-first with numeric keypad hints and is tested down to a 320-pixel viewport with no horizontal scrolling.
Can I use it offline?
Largely, yes. Because computation is client-side, the page continues to calculate without a network connection once it has loaded.
Which currency does it use?
Amounts display in US$ accounting format, but the underlying mathematics is currency-agnostic. The result is identical in any currency, so simply read the figures in your own.
Why does a result show an em-dash?
An em-dash indicates the calculation is not defined for the inputs given — typically a division by zero or a value outside the valid domain. We show a dash rather than a misleading number.
How do I report an error?
Email apexconverter.praxiscalc@gmail.com with the tool URL, your exact inputs, the output received and the output you expected. Verified mathematical errors are patched within 72 hours.