Pressure is force distributed over area, but the unit you use depends on the industry: tire gauges in the United States often read psi, vehicle placards and engineering sheets use kPa or bar, weather reports use hectopascals or millibars, chemistry uses atmospheres, and barometers and medical contexts use mercury columns. The pressure converter is the general hub that keeps pascals, kilopascals, bar, atmospheres, psi, and mmHg in one place. The barometric pressure conversion is the weather-facing page that adds hPa, mbar, and inches of mercury and keeps full-precision mercury constants. Both convert through pascals; they differ in units, factors, and context.
What each calculator does
The pressure converter lets you choose any source and target pair among pascals, kilopascals, bar, standard atmospheres, pounds per square inch, and millimeters of mercury. It converts the source value to pascals first — using factors 1 for Pa, 1,000 for kPa, 100,000 for bar, 101,325 for atm, 6,894.76 for psi, and 133.322 for mmHg — then divides by the target factor. The primary result shows the selected conversion and the detail rows show the same input in every supported unit. Its page explains that psi and mmHg factors are rounded in this hub, so results may differ in the last few decimals from specialized pages that store longer constants, and it covers gauge-versus-absolute interpretation.
The barometric pressure conversion supports pascals, hectopascals, kilopascals, millibars, bars, atmospheres, millimeters of mercury, inches of mercury, and pounds per square inch. Hectopascals and millibars both equal 100 Pa, so they convert one-to-one. The mercury factors are the conventional 0 °C constants — mmHg 133.322387415 Pa and inHg 3386.388640341 Pa — and psi is derived from the exact pound-force, standard-gravity, and inch definitions, about 6,894.757293168 Pa. The default example converts 1013.25 hPa to 29.9213 inHg, and the page notes it performs unit conversion only, not sea-level reduction or altitude correction.
Side-by-side
| Pressure converter | Barometric pressure conversion | |
|---|---|---|
| Units | Pa, kPa, bar, atm, psi, mmHg | Pa, hPa, mbar, kPa, bar, atm, mmHg, inHg, psi |
| Mercury factors | Rounded: mmHg 133.322 Pa | Conventional 0 °C: mmHg 133.322387415 Pa, inHg 3386.388640341 Pa |
| Psi factor | Rounded: 6,894.76 Pa | Derived from exact definitions: about 6,894.757293168 Pa |
| Standard atmosphere | Exactly 101,325 Pa | Exactly 101,325 Pa (1013.25 hPa) |
| Example | 35 psi = 241.316600 kPa | 1013.25 hPa = 29.9213 inHg |
| Focus | General engineering and everyday pairs | Weather, barometers, altimeter settings |
| Reference guidance | Gauge vs absolute pressure | Gauge vs absolute; station vs sea-level pressure |
When to use which
Use the pressure converter for the general pair when the units are already fixed — a U.S. tire gauge read in psi that needs kPa for a metric placard, a compressor rating in bar, a chemistry problem in atmospheres, or a vacuum reading in mmHg. It is deliberately broad, and its rounded psi and mmHg factors are appropriate for general conversion work.
Use the barometric pressure conversion when the reading is an atmospheric pressure in weather, aviation, or instrument language: converting a 997 hPa forecast, an inHg altimeter setting for a U.S. pilot, or a lab record in mmHg. Its full-precision mercury constants and the hPa-mbar equivalence matter when small pressure changes must not be hidden by rounding, especially near standard sea-level pressure.
Both pages warn that conversion does not change a pressure’s reference. A gauge value measured above local air pressure and an absolute value measured from a vacuum can share a unit but describe different physical references, and converting barometric pressure does not adjust for elevation. Keep the gauge or absolute label attached afterward.
Limits and disclaimer
The pressure converter’s psi and mmHg factors are rounded, so its last decimals can differ from pages that store longer constants; keep extra digits for chained calculations and round only to the precision justified by the source. The barometric page’s mercury values are conventional 0 °C constants, and 760 mmHg is only approximately 1 atm under them. Neither calculator performs sea-level reduction, altitude correction, or gauge-to-absolute adjustment, and neither makes a converted number more precise than the original measurement.