Pressure Converter Calculator

The Pressure Converter Calculator is the multi-unit hub for the pressure family. It converts among pascals, kilopascals, bar, standard atmospheres, pounds per square inch, and millimeters of mercury. Unlike a unit-family page such as PSI conversion or pascal conversion, this hub lets you choose both the source unit and the target unit. Use it when you need a one-off pair such as psi to kPa, mmHg to Pa, atm to bar, or kPa to mmHg.

Pressure is force distributed over area, but different industries speak different unit languages. Tire gauges in the United States often use psi. Vehicle placards and engineering sheets may use kPa or bar. Weather reports commonly use hectopascals or millibars, which connect directly to Pa and bar. Chemistry and gas-law examples often use atm. Vacuum and medical contexts often use mmHg. The hub keeps those units in one place while preserving the original pressure reference.

How to use the pressure hub

Enter a nonnegative pressure value, choose the source unit, and choose the target unit. The primary result shows the selected conversion. The detail rows show the same input converted to every supported pressure unit, so you can quickly compare whether a specification is closer to a tire pressure, an atmosphere, a bar-level equipment rating, or a vacuum-style mmHg value.

Use bar to PSI for the common tire and compressor pair, kPa to psi conversion for metric tire placards, and ATM conversion for standard-atmosphere source values. For mechanics problems where pressure comes from force over area, a separate force converter may be useful before you calculate pressure.

Unit definitions

The pascal is the SI derived pressure unit:

$1\ \text{Pa} = 1\ \frac{\text{N}}{\text{m}^{2}}$

Kilopascal is the pascal scaled by one thousand:

$1\ \text{kPa} = 1{,}000\ \text{Pa}$

Bar is a decimal pressure unit:

$1\ \text{bar} = 100{,}000\ \text{Pa}$

Standard atmosphere is an exact reference:

$1\ \text{atm} = 101{,}325\ \text{Pa}$

The calculator also supports psi and mmHg using the stated pascal factors. Psi is pounds per square inch and mmHg is millimeters of mercury.

Formula used by the calculator

The hub converts the source value to pascals first:

$\text{value in Pa} = \text{input value} \times \text{source factor in Pa}$

Then it divides by the selected target factor:

$\text{target value} = \frac{\text{value in Pa}}{\text{target factor in Pa}}$

The calculator uses these factors:

The psi and mmHg factors are rounded in this hub’s calculation, so the results are appropriate for general conversion but may differ in the last few decimals from more specialized pages that store longer constants.

Worked example: 35 psi to kPa

Set the value to 35, choose psi as the source unit, and choose kPa as the target unit. The calculator first converts psi to pascals using the hub factor:

$35 \times 6{,}894.76 = 241{,}316.6\ \text{Pa}$

Then it converts pascals to kilopascals:

$\frac{241{,}316.6}{1{,}000} = 241.3166\ \text{kPa}$

Because kPa is formatted to six decimal places, the selected result is 241.316600 kPa. The detail rows use the same full dimensional psi factor and conventional 0 °C mmHg factor as the calculation.

Reference table

Choosing the right pressure unit

Use pascals when working directly with SI formulas involving newtons and square meters. Use kPa for readable gas, weather, tire, and low-pressure engineering values. Use bar for compressors, scuba cylinders, process equipment, and many pressure gauges. Use atm when comparing to a conventional atmosphere in chemistry or pressure-ratio examples. Use psi when reading U.S. tire gauges, plumbing gauges, air tools, or pressure washers. Use mmHg for barometers, vacuum instruments, or medical readings where that convention is still expected.

The hub is deliberately broad, but focused pages can be clearer when a unit is already known. For instance, bar to atm conversion explains why one bar is slightly less than one atmosphere, while pascal conversion spends more time on Pa, kPa, and MPa.

Gauge pressure, absolute pressure, and precision

The most important interpretation issue is not the conversion factor; it is the reference point. Gauge pressure is measured above local atmospheric pressure. Absolute pressure is measured from a vacuum. A tire at 35 psig is not 35 psia. If a calculation requires absolute pressure, you may need to add local atmospheric pressure before converting or comparing. The exact offset depends on the local barometric pressure, which changes with weather and altitude.

Precision should also follow the source. A pressure washer advertised at 2,000 psi is not known to six meaningful decimals after conversion. Keep the extra digits for internal comparison, then round for the instrument, tolerance, or specification you are using.

Accuracy and limits

The calculator keeps the defined or cited relationship through the calculation and rounds only the displayed result. A converted number does not become more precise than the source measurement. Keep additional digits for chained calculations, then round to the precision justified by the original value; also preserve any reference basis or notation convention named with the input.

Sources

• NIST, SI Units — SI context for pascal pressure units.
• NIST, Special Publication 811 — unit conversion and SI usage guidance.
• NOAA Ocean Service, What is a barometer? — barometric pressure context.