Pressure Conversion

Convert pressure between bar, psi, atmospheres, pascals, and more.

Supports 15 pressure units with bidirectional conversion and selectable display units.

Updated August 8, 2026

CreatorFrank Zhao

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Introduction / overview

Pressure Conversion turns a single pressure value into its equivalent in the units people actually meet — bar, pounds per square inch (psi), atmospheres, pascals, and a full set of extras from micropascals up to gigapascals, including torr, millimetres and inches of mercury, and the technical atmosphere.

Type a value in any field and every other unit updates at once, in either direction — no formulas to juggle when a manual says bar but your gauge reads psi.

It is the kind of tool you reach for when a tyre spec lists bars but the pump gauge shows psi, when a weather report quotes hectopascals and you want atmospheres, or when an engineering datasheet uses megapascals and you need pounds per square inch. All fifteen units describe the same physical pressure, so nothing else has to be typed.

How to use / quick start

1Find the field whose unit matches the value you have — bar, psi, atmospheres, or pascals in the top section, or pick any extra unit in “More conversion options”.
2Type the number. Every other field recalculates instantly to the same pressure.
3Read the unit you need. If the “Other pressure units” field is showing a different unit than you want, switch it with the selector on the right.

Example: a car spec of 2.4 bar on a psi gauge

Enter $2.4$ in the “Pressure in bar” field. The converter converts through pascals, then to pounds per square inch:

2.4

\ \mathrm{bar}

\times

100{,}000

\ \mathrm{Pa/bar}

=

240{,}000

\ \mathrm{Pa}

240{,}000

\ \mathrm{Pa}

\div

6{,}894.757

\ \mathrm{Pa/psi}

\approx

34.8091

\ \mathrm{psi}

The same entry also reads $2.36862\ \mathrm{atm}$ , $240\ \mathrm{kPa}$ , and $240{,}000\ \mathrm{Pa}$ , so you can see every equivalent in one pass.

Example: a 100 psi bike tyre in bar and kPa

You can start from any unit. Enter $100$ in the “Pressure in pounds per square inch” field and read the metric equivalents:

100

\ \mathrm{psi}

\times

6{,}894.757

\ \mathrm{Pa/psi}

\approx

689{,}475.7

\ \mathrm{Pa}

689{,}475.7

\ \mathrm{Pa}

\div

100{,}000

\approx

6.89476

\ \mathrm{bar}

That is about $6.89\ \mathrm{bar}$ or $689.5\ \mathrm{kPa}$ — the same pressure, just a different unit.

Calculation method

Every field is converted through the pascal, the SI derived unit of pressure built from the base units metre, kilogram, and second: one pascal is one newton per square metre.

If $P_s$ is the value you entered and $f_s$ is the number of pascals in one source unit, the shared pressure is:

P_{\mathrm{Pa}} = P_s \times f_s

P_t

=

P_{\mathrm{Pa}} \div f_t

=

P_s \times \frac{f_s}{f_t}

The conversion factors are exact definitions: $1\ \mathrm{bar} = 100{,}000\ \mathrm{Pa}$ , $1\ \mathrm{atm} = 101{,}325\ \mathrm{Pa}$ , and $1\ \mathrm{psi} = \frac{4.4482216152605}{0.0254^2}\ \mathrm{Pa}$ (one pound-force on one square inch). Because every field stores pascals, the same relationship works in reverse — you can enter any field and the rest follow.

How to read the method:

$P_{\mathrm{Pa}}$ is the shared pressure expressed in pascals.
$f_s$ and $f_t$ are the pascals-per-unit factors for the source and target units, such as $100{,}000\ \mathrm{Pa/bar}$ or $101{,}325\ \mathrm{Pa/atm}$ .
You can enter any editable field, so the conversion runs in both directions rather than only from pascals outward.

Real-world examples

Reading a weather report in familiar units

A station reports $1013\ \mathrm{hPa}$ , the standard sea-level pressure. Enter it in the “Other pressure units” field with hectopascals selected:

1013

\ \mathrm{hPa}

=

1013

\times

100\ \mathrm{Pa}

=

101{,}300

\ \mathrm{Pa}

\approx

0.999753

\ \mathrm{atm}

=

29.92

\ \mathrm{inHg}

If your barometer or the aviation weather text uses inches of mercury, the same reading is about $29.92\ \mathrm{inHg}$ — a number you will recognise from “30.00 inHg” being a fair-weather benchmark.

High-pressure equipment: a scuba cylinder at 200 bar

A dive cylinder filled to $200\ \mathrm{bar}$ is rated in different units by different manufacturers:

200

\ \mathrm{bar}

=

20{,}000{,}000

\ \mathrm{Pa}

=

2{,}900.75

\ \mathrm{psi}

=

20

\ \mathrm{MPa}

Switching the “Other pressure units” selector between kPa and MPa shows the same fill as $20{,}000\ \mathrm{kPa}$ or $20\ \mathrm{MPa}$ , so you can compare cylinder and compressor ratings written in either system.

Vacuum work: a gauge below atmospheric pressure

A vacuum pump pulls a gauge pressure of $-0.5\ \mathrm{bar}$ (half a bar below the surrounding air). The converter keeps the sign so the vacuum stays visible:

-0.5

\ \mathrm{bar}

\times

100{,}000

\ \mathrm{Pa/bar}

=

-50{,}000

\ \mathrm{Pa}

=

-7.25189

\ \mathrm{psi}

A value below the reference is a perfectly valid gauge reading — it tells you how far below atmospheric pressure the system is, which is how vacuum gauges are usually scaled.

Related concepts

Fifteen units, three families

The units fall into a few families with distinct jobs:

SI pascals and multiples — Pa, kPa, MPa, GPa, hPa, mbar, mPa, µPa — used from weather (hPa) to structural engineering (MPa, GPa).
Atmosphere and bar — bar (100,000 Pa) and mbar sit alongside the standard atmosphere (atm). A millibar is numerically identical to a hectopascal, which is why weather reports use either name.
Imperial and mercury units — psi (pounds per square inch), inches of mercury (inHg), millimetres of mercury (mmHg), and torr, common in US tools, aviation, barometers, and vacuum systems.

Unit	In pascals	Typical use
$\mathrm{bar}$	100,000 Pa	Tires, industry, and everyday metric pressure
$\mathrm{atm}$	101,325 Pa	Sea-level reference; chemistry and scuba
$\mathrm{psi}$	≈ 6,894.757 Pa	Tires and tools in the US / imperial world
$\mathrm{Pa}$	1 Pa	The SI unit — one newton per square metre
$\mathrm{kPa}$	1,000 Pa	Engineering and appliance specs
$\mathrm{MPa}$	1,000,000 Pa	Structural and high-pressure engineering
$\mathrm{GPa}$	1,000,000,000 Pa	Materials science (modulus, strength)
$\mathrm{hPa}$	100 Pa	Weather reports and barometers
$\mathrm{mbar}$	100 Pa	Same as hPa — meteorology and vacuum work
$\mathrm{Torr}$	101,325 ÷ 760 Pa	Vacuum systems and lab work
$\mathrm{mmHg}$	133.322387415 Pa	Blood pressure and lab gauges
$\mathrm{inHg}$	≈ 3,386.389 Pa	Aviation and US barometers
$\mathrm{at}$	98,066.5 Pa	kgf/cm² in older metric engineering
$\mathrm{mPa}$	0.001 Pa	Very low pressures in science
$\mathrm{uPa}$	0.000001 Pa	Acoustics and micro-pressure studies

Gauge vs. absolute pressure

A gauge measures pressure relative to the surrounding air, so a reading of $0\ \mathrm{bar}$ simply means “equal to atmospheric pressure”, not “no pressure at all”. Absolute pressure counts from a true vacuum, so it is always roughly $1.013\ \mathrm{bar}$ higher than a gauge reading at sea level. This converter converts whatever number you type — if your gauge shows a value below its reference, enter it as a negative number and the sign is preserved.

Two “atmospheres” that are not the same

The standard atmosphere ( $\mathrm{atm}$ ) is the sea-level reference of $101{,}325\ \mathrm{Pa}$ . The technical atmosphere ( $\mathrm{at}$ ) is one kilogram-force per square centimetre, $98{,}066.5\ \mathrm{Pa}$ . They differ by about $3.2\%$ , so treating them as interchangeable can quietly shift results.

Frequently asked questions

Is the technical atmosphere (at) the same as the standard atmosphere (atm)?

No. $\mathrm{atm}$ is $101{,}325\ \mathrm{Pa}$ , while $\mathrm{at}$ is one kilogram-force per square centimetre, $98{,}066.5\ \mathrm{Pa}$ — about $3.2\%$ smaller. The technical atmosphere turns up in older metric engineering; the standard atmosphere is the common sea-level reference in chemistry and diving.

Are torr and mmHg the same thing?

Very close, but not identical. One torr is exactly one 760th of a standard atmosphere, about $133.32237\ \mathrm{Pa}$ , while one millimetre of mercury (at 0 °C) is $133.322387415\ \mathrm{Pa}$ . They agree to roughly five significant figures, so the difference only matters in high-precision vacuum work.

Can I enter a negative value for a vacuum?

Yes. A gauge below its reference — such as a vacuum pump at $-0.5\ \mathrm{bar}$ — is a valid pressure, and the converter keeps the sign. Entering $-0.5$ in the bar field reads $-50{,}000\ \mathrm{Pa}$ and about $-7.25\ \mathrm{psi}$ , which is how far below atmospheric pressure the system sits.

Limitations

•This tool converts the pressure you type; it does not add or subtract atmospheric pressure for you. Gauge and absolute readings are only equivalent once you account for the reference yourself.
•The millimetre- and inch-of-mercury values use the conventional 0 °C mercury definition. A real mercury column expands with temperature, so its reading drifts slightly outside that reference.
•For safety-related use — scuba, pressure vessels, medical equipment — confirm values against certified gauges and the applicable standards; unit conversion alone does not replace equipment calibration.

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