Pressure Unit Conversion: Pa, bar, psi and More

Pressure unit conversion changes a pressure reading from one unit to another without changing the physical pressure. Enter a value and choose its starting and target units to get the equivalent pressure, with common choices including pascals, kilopascals, bar, atmospheres, and pounds per square inch.

Formula

Convert through pascals, the SI unit of pressure: target value = input value × source-unit factor ÷ target-unit factor. The factors are the number of pascals represented by one unit.

• Input value is the pressure entered, in the chosen source unit.
• Source-unit factor converts that unit to pascals.
• Target-unit factor is the number of pascals in one target unit.
• Converted pressure is the equivalent pressure in the selected target unit.

For example, 1 bar × 100,000 Pa/bar ÷ 6,894.757293168 Pa/psi gives about 14.50 psi. The conversion factors in the calculator are: 1 Pa = 1 Pa; 1 kPa = 1,000 Pa; 1 MPa = 1,000,000 Pa; 1 bar = 100,000 Pa; 1 standard atmosphere (atm) = 101,325 Pa; and 1 psi = 6,894.757293168 Pa.

Worked Example

The default input is 101,325 Pa, converted to pascals. The selected source and target factors are both 1 Pa per Pa.

1. Multiply the input by the source factor: 101,325 × 1 = 101,325 Pa.
2. Divide by the target factor: 101,325 ÷ 1 = 101,325 Pa.
3. At two decimal places, the result is 101,325.00 Pa.

Choosing another target unit changes the displayed unit and number, not the underlying pressure. For instance, 101,325 Pa is 101.325 kPa, 1.01325 bar, 1 atm, or about 14.70 psi.

What Pressure Units Measure

Pressure is force distributed over an area. In the SI system, one pascal (Pa) equals one newton per square metre (N/m²). Because a pascal is small for many everyday readings, pressure is often expressed in kilopascals (kPa) or megapascals (MPa): 1 kPa is 1,000 Pa, and 1 MPa is 1,000,000 Pa.

Other units remain common in particular settings. The bar is widely used for many technical and weather-related readings, while psi—pounds-force per square inch—is familiar in the United States. The atmosphere (atm) is a reference unit defined as exactly 101,325 Pa. It is close to, but not identical to, the bar: 1 bar is 100,000 Pa.

Pressure units may also include millibars (mbar), commonly used in meteorology, and millimetres of mercury (mmHg), often seen in scientific and instrument contexts. Since 1 mbar equals 100 Pa, 1,000 mbar equals 1 bar. The calculator’s listed units cover common conversions; for units not listed, first find a reliable conversion factor to pascals.

How to Convert a Reading

Use the calculator by entering the number as it appears in the source unit, then selecting both units. Its result is rounded to two decimal places, so retain more precision if a later calculation or specification requires it.

1. Check the original unit on the gauge, instrument, data sheet, or measurement.
2. Enter the numerical reading without adding the unit to the number.
3. Select the source unit and the unit you need.
4. Read the result together with its target unit; never copy the number alone.

As a check, converting from a smaller unit to a larger one generally makes the numerical value smaller. Thus 200 kPa becomes 0.2 MPa, while 2 bar becomes 200 kPa. Converting back should recover the starting value apart from rounding.

Absolute and Gauge Pressure

A unit conversion changes the scale, not the kind of pressure being reported. This matters because pressure can be stated as absolute pressure or gauge pressure. Absolute pressure is measured relative to a perfect vacuum. Gauge pressure is measured relative to the surrounding atmospheric pressure; a tyre gauge, for example, generally reports pressure above the local atmosphere.

To compare these readings correctly, identify their reference. In the usual convention, absolute pressure equals gauge pressure plus local atmospheric pressure. A gauge reading of zero does not mean there is no pressure: it means the measured pressure matches the surrounding atmosphere. Converting a gauge value from psi to kPa does not turn it into an absolute value.

Common Errors and Precision

• Confusing bar and atm: they are close but differ by 1,325 Pa per unit.
• Mixing gauge and absolute values: matching units alone does not make readings directly comparable.
• Dropping prefixes: kPa and MPa differ by a factor of 1,000.
• Rounding too early: keep full precision through intermediate steps, then round the final answer to the precision appropriate for the measurement.
• Ignoring context: a pressure limit or instrument reading may specify a particular unit and reference; preserve those labels when recording results.

Conversion factors do not make a measurement more accurate. If the original instrument is uncertain, extra decimal places in the converted answer are only arithmetic detail. Follow the precision and unit conventions required by the equipment or calculation you are using.

Frequently Asked Questions

How many kPa are in 1 bar?
One bar is exactly 100 kPa, because 1 bar equals 100,000 Pa and 1 kPa equals 1,000 Pa.

How many psi are in 1 bar?
One bar is approximately 14.5038 psi. The exact displayed value can vary slightly with rounding.

Is 1 atm the same as 1 bar?
No. One standard atmosphere is 101,325 Pa, while one bar is 100,000 Pa. They are similar, but not equal.

How do I convert kPa to psi?
Multiply kPa by approximately 0.1450377 to obtain psi. For example, 100 kPa is about 14.50 psi.

Why does a pressure gauge read zero when pressure is present?
A gauge-pressure instrument uses the surrounding atmosphere as its zero reference. A zero gauge reading corresponds to local atmospheric pressure in absolute terms, not a vacuum.

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in pressure | Pressure value | Pa | 101325 | 0
sel from | Convert from | Pa=1, kPa=1000, MPa=1000000, bar=100000, atm=101325, psi=6894.757293168
sel to | Convert to | Pa=1, kPa=1000, MPa=1000000, bar=100000, atm=101325, psi=6894.757293168
out converted | Converted pressure | selected unit | pressure * from / to | 2