What this calculator does
Change a pressure from one unit to another, such as the psi on your tire gauge into kilopascals. Pressure turns up in many fields, and each tends to use its own unit. Tire gauges use psi (pounds per square inch). Weather maps use hectopascals or millibars. Diving and factory equipment use bar. Blood pressure uses millimeters of mercury, and physics uses pascals.
They all measure the same thing: force spread over an area. So any of them can be changed into any other.
Enter a pressure and choose the two units. The converter gives the result and shows the working, which goes through pascals. You also get a table of the same pressure in all ten units.
Where it's used
Why this math matters outside the classroom:
- Barometers. A barometer reading of 30.00 inHg is about 1,016 hPa.
- Diving. Every 10 m of seawater adds roughly 1 bar of pressure, about 14.5 psi.
- Tires. A 32 psi tire pressure is about 2.2 bar, or 221 kPa.
- Vacuum pumps. A lab vacuum of 1 torr is a pressure of about 133 Pa.
- Standard atmosphere. One atmosphere equals 101,325 Pa, 760 mmHg and about 14.7 psi.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.RP.A.3.d. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Enter the pressure. Zero and decimals are allowed; negative values aren't.
- Choose the unit you're converting from and the unit you want.
- Read the result or check the table. The working shows the size of each unit in pascals.
What the inputs mean
- Pressure
- The pressure to convert, in the “From” unit. Gauge readings (pressure above the air around you) and absolute readings convert the same way. The tool doesn't add or remove the pressure of the air itself.
- From
- The unit your number is in. Hectopascals and millibars are the same size, so they share one entry.
- To
- The unit you want the answer in.
Formula and method
result = value × (from-unit in Pa) ÷ (to-unit in Pa) 1 bar = 100,000 Pa; 1 hPa = 1 mbar = 100 Pa 1 atm = 101,325 Pa; 1 torr = 101,325 ÷ 760 Pa 1 psi = 1 lbf/in² ≈ 6,894.757 Pa 1 mmHg ≈ 133.322387 Pa; 1 inHg = 25.4 mmHg ≈ 3,386.389 Pa
The converter first turns your value into pascals (Pa), then into the unit you want. Pa is the pascal, hPa the hectopascal and mbar the millibar. atm is the standard atmosphere, the usual air pressure at sea level. psi is pounds per square inch, and lbf/in² is the same thing written out: pound-force per square inch. mmHg and inHg are millimeters and inches of mercury.
The pascal is one newton (a unit of force) per square meter. The bar and the standard atmosphere are each set as an exact number of pascals. The psi follows from the exact pound and inch, together with standard gravity, 9.80665 m/s².
Millimeters and inches of mercury describe the pressure under a column of mercury of a set height. The usual values used here assume a mercury density of 13,595.1 kg/m³ and standard gravity. The torr is exactly 1/760 of an atmosphere. That makes it differ from the millimeter of mercury by less than one part in seven million.
Worked example
A tire placard says 30 psi. What is that in kilopascals?
- 30 psi × 6,894.757293 Pa = 206,842.718795 Pa.
- 206,842.718795 Pa ÷ 1,000 = 206.842719 kPa.
Result: 30 psi is about 206.84 kPa, or roughly 2.07 bar.
Understanding the result
Standard air pressure at sea level is 1 atm. That's 101.325 kPa, 1,013.25 hPa, about 14.7 psi, and 760 mmHg.
Tire gauges and many factory gauges read gauge pressure, meaning pressure above the surrounding air. Converting units doesn't change whether a reading is gauge or absolute, so keep track of which one you have.
Assumptions and limitations
- psi is pound-force per square inch, with standard gravity of 9.80665 m/s².
- mmHg and inHg use the usual mercury density of 13,595.1 kg/m³.
- It doesn't convert between gauge and absolute pressure.
- Negative values, such as vacuum gauge readings, aren't accepted.
- Units such as inches of water, kgf/cm² and ksi aren't included.
Frequently asked questions
Are millibars and hectopascals the same?
Yes. Both equal exactly 100 pascals. Weather forecasters switched from millibars to hectopascals, so the numbers on weather maps could stay the same.
What is the difference between torr and mmHg?
The torr is exactly 1/760 of a standard atmosphere. The usual millimeter of mercury is worked out from mercury's density and standard gravity. The two differ by about 0.000014%. That only matters in very precise lab measurement.
How many psi is one bar?
About 14.504 psi. One bar is a little less than one standard atmosphere, which is about 14.696 psi.
Why do weather reports in the US use inches of mercury?
It comes from the mercury barometers once used to measure air pressure. A typical sea-level reading is about 29.92 inHg, which equals 1,013.25 hPa.
Is there a page for a single pair, such as psi to bar?
Yes. The two pairs that come up most with tires, compressors and gauges have their own pages, with a reference table: psi to bar and kilopascals to psi.
How this calculator is checked
Method: SI pascal; bar = 10⁵ Pa and atm = 101,325 Pa by definition; psi from the international pound and inch with g = 9.80665 m/s²; conventional mmHg (13,595.1 kg/m³ mercury); torr = atm/760. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
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