Pressure Converter
Example 1
A driver in Europe checks their tyre pressure and the gauge reads 220 kPa. The owner’s manual for their American-made car specifies tyre pressure in psi (pounds per square inch). The driver needs to convert 220 kPa to psi for correct inflation.
Solution
The conversion from kilopascals to psi uses the factor 1 kPa = 0.145038 psi. Multiplying: 220 kPa × 0.145038 psi/kPa = 31.908 psi.
Rounding to the nearest whole psi gives 32 psi, which is a common recommendation for passenger car tyres. For mental estimation, dividing kPa by 7 gives a rough equivalent: 220 ÷ 7 ≈ 31.4 psi, within 2 per cent of the exact value. The reverse approximation, multiplying psi by 7 to get kPa, is also useful. Proper tyre pressure affects fuel economy, tyre life, and vehicle safety.
Answer
31.9 psi (32 psi rounded). A tyre pressure of 220 kPa converts to approximately 32 psi, which is standard for most passenger vehicles.
Source: US National Highway Traffic Safety Administration: Tyre Safety
Example 2
A weather report in the United States states that atmospheric pressure is 29.92 inches of mercury (inHg). A meteorologist in Europe needs this value in millibars (mbar) for an international weather model that uses metric units.
Solution
The conversion from inches of mercury to millibars uses the factor 1 inHg = 33.8639 mbar. Multiplying: 29.92 inHg × 33.8639 mbar/inHg = 1,013.25 mbar.
Standard atmospheric pressure at sea level is 1,013.25 mbar, 29.92 inHg, or 101.325 kPa. This value is used as the reference point for altimeter calibration in aviation. If the reported pressure is below 1,013 mbar, it indicates a low-pressure system associated with storms. If above, a high-pressure system with fair weather. Meteorologists track these differences in millibars to forecast weather patterns.
Answer
1,013.25 mbar. Standard sea-level atmospheric pressure of 29.92 inHg equals 1,013.25 mbar, which is the benchmark for weather analysis and aviation altimeter settings worldwide.
Source: World Meteorological Organization: Guide to Meteorological Instruments
Example 3
A patient’s blood pressure reading is 120/80 mmHg. A medical researcher compiling data for an international study needs these values converted to kilopascals (kPa), the SI unit for pressure used in scientific publications.
Solution
The conversion uses the factor 1 mmHg = 0.133322 kPa. For systolic pressure (120 mmHg): 120 mmHg × 0.133322 kPa/mmHg = 15.999 kPa. For diastolic pressure (80 mmHg): 80 mmHg × 0.133322 kPa/mmHg = 10.666 kPa.
Rounding to one decimal place gives 16.0/10.7 kPa. The standard reference range for healthy blood pressure is below 120/80 mmHg (16.0/10.7 kPa). Medical professionals worldwide use mmHg for clinical measurements, but research journals increasingly require SI units. This dual-unit reporting is common in international cardiology studies and WHO health reports.
Answer
16.0/10.7 kPa. A blood pressure reading of 120/80 mmHg converts to 16.0/10.7 kPa, representing normal healthy blood pressure by international standards.
Example 4
A driver finds tyres at 32 psi. The manual lists pressure in kPa. Convert to kPa and bar.
Solution
1 psi = 0.068948 bar. 32 × 0.068948 = 2.21 bar.
Answer
32 psi = 220.6 kPa = 2.21 bar. Standard range: 30–35 psi.
Source: NHTSA: Tyre Safety
Published:
Updated:
References
- [1]National Institute of Standards and Technology (NIST), Guide for the Use of the International System of Units (SI), 2008. https://physics.nist.gov/cuu/pdf/sp811.pdf
- [2]International Organization for Standardization, ISO 80000-4: Quantities and Units – Part 4: Mechanics, 2019.
- [3]Bureau International des Poids et Mesures (BIPM), The International System of Units (SI) – 9th Edition, 2019. https://www.bipm.org/en/publications/si-brochure
Glossary
- Pressure – Force applied perpendicular to a surface per unit area, measured in pascals (Pa) in the SI system. Pressure is a scalar quantity that describes the distribution of force across a surface.
- Pascal (Pa) – The SI unit of pressure, defined as one newton per square metre (N/m²). One kilopascal (kPa) equals 1,000 Pa and is commonly used for tyre pressure and atmospheric measurements.
- Bar – A metric unit of pressure equal to 100,000 Pa, approximately equal to atmospheric pressure at sea level. The millibar (mbar) is widely used in meteorology worldwide.
- PSI (pounds per square inch) – The imperial unit of pressure, measuring the force in pounds applied to one square inch of area. PSI is the standard unit for tyre pressure in the United States and for hydraulic systems.
- Atmosphere (atm) – A unit of pressure defined as exactly 101,325 Pa, equal to average atmospheric pressure at sea level. The atmosphere is used in chemistry, diving, and engineering contexts.
- mmHg (millimetres of mercury) – A unit of pressure based on the height of a mercury column in a manometer. It is the standard unit for blood pressure measurement and is commonly used in vacuum systems and barometers.
- Torr – A unit of pressure defined as 1/760 of an atmosphere, nearly identical to 1 mmHg. The torr is used in vacuum science, with 1 torr ≈ 133.322 Pa.
- Gauge pressure vs absolute pressure – Gauge pressure measures pressure relative to atmospheric pressure, while absolute pressure measures total pressure including the atmosphere. Tyre pressure gauges read gauge pressure; scientific calculations use absolute pressure.
- Hydrostatic pressure – The pressure exerted by a fluid at rest due to gravity, calculated as ρgh (density × gravity × depth). Hydrostatic pressure is fundamental to hydraulic systems, dam design, and blood circulation.
- Standard atmospheric pressure – The average pressure of Earth’s atmosphere at sea level, defined as 101,325 Pa, 1,013.25 mbar, 29.92 inHg, or 14.696 psi. It serves as the reference point for altimeters, pressure gauges, and weather reporting.
How to Use?
- 1
Enter the pressure value
Type the numeric pressure amount into the Pressure Value field.
- 2
Select the source unit
Choose the unit of your input value from the unit dropdown: Pa, kPa, MPa, bar, psi, atm, or mmHg.
- 3
Choose the display unit
Use the Display Result In dropdown to select which unit appears highlighted as the primary result.
- 4
Review all equivalent values
The result panel shows your value in the chosen display unit, with all other supported units listed as alternatives below.
- 5
Check gauge vs absolute
Remember that this converter uses absolute pressure (pascals as base). Enter the absolute pressure value, not the gauge reading. For a gauge reading, add atmospheric pressure first.
- 6
Use related converters
For area unit conversions, use the Area Converter linked on this page. The Energy Converter handles thermodynamic PV work calculations.
Frequently Asked Questions
psi stands for pounds per square inch, a unit of pressure common in tyre pressure gauges, hydraulic systems, and HVAC refrigerant measurements in the United States. One psi equals approximately 6,894.76 Pa. Typical car tyre pressures range from 30 to 35 psi.
1 atm = 101.325 kPa exactly, defined as the average atmospheric pressure at sea level on Earth. It is used as a reference for pressure measurements in diving, aviation, chemistry, and physics. One atmosphere supports a 760 mm column of mercury in a barometer.
1 bar = 100 kPa exactly. This simple decimal relationship makes conversion between bar and kPa straightforward: multiply bar by 100 to get kPa, or divide kPa by 100 to get bar. Standard atmospheric pressure is 1.01325 bar or 101.325 kPa.
mmHg (millimetres of mercury) originated from the mercury manometer invented by Evangelista Torricelli in 1643. Normal blood pressure is around 120/80 mmHg. The measurement persists due to medical convention and the vast body of clinical research and treatment guidelines that reference mmHg. Converting to kPa is straightforward: multiply mmHg by 0.133322 to get kPa.
1 atm = 14.696 psi at sea level. For everyday use, 14.7 psi is a common approximation. This value is important for understanding gauge versus absolute pressure: a tyre gauge reading of 0 psi actually measures 14.7 psi absolute because the gauge reads relative to the surrounding atmosphere.
Absolute pressure (psia) includes atmospheric pressure, while gauge pressure (psig) measures pressure relative to the atmosphere. A tyre pressure reading of 32 psi is gauge pressure, so the absolute pressure inside is about 46.7 psi at sea level. This converter uses absolute pressure in pascals as the base, so gauge readings need to be adjusted by adding atmospheric pressure (14.7 psi or 101.325 kPa) before entering the value.
Atmospheric pressure decreases with altitude exponentially. At sea level it is 1013.25 hPa (1 atm). At 1,500 m elevation it drops to about 845 hPa. At 3,000 m it is around 700 hPa. At 5,500 m (Mount Everest base camp) it is approximately 500 hPa. This affects everything from cooking times to aircraft performance to tyre pressure readings.
Normal blood pressure is around 120/80 mmHg, which equals about 16.0/10.7 kPa. The systolic (top) number measures pressure when the heart contracts, while diastolic (bottom) measures pressure between beats. Hypertension is diagnosed at readings consistently above 140/90 mmHg (18.7/12.0 kPa). Always consult a healthcare professional for interpretation.
One bar equals 100,000 Pa (exactly 100 kPa), while one standard atmosphere equals 101,325 Pa. They are close but not equal: 1 bar = 0.987 atm, and 1 atm = 1.01325 bar. The 1.325% difference matters in precision applications such as laboratory calibration, aerospace engineering, and pharmaceutical manufacturing.
Megapascal (MPa) equals 1,000,000 Pa or 1,000 kPa. It is the standard unit for material strength specifications such as steel yield strength (250 to 1,500 MPa), concrete compressive strength (20 to 40 MPa for standard mixes), and high-pressure hydraulic systems. One MPa equals approximately 145 psi.
Tyre pressure increases approximately 1 psi for every 5.5°C (10°F) temperature rise. Cold tyres (after sitting overnight) read lower than hot tyres (after highway driving). Always check and adjust tyre pressure when the tyres are cold, following the manufacturer's recommended cold pressure. Releasing air from hot tyres to reach the cold specification results in under-inflation once they cool down.
mmHg stands for millimetres of mercury, representing the height of a mercury column in a manometer or barometer. It remains in use due to medical convention for blood pressure measurement (millions of clinical studies reference mmHg), aviation altimeter settings in some countries, and vacuum measurement in laboratory equipment. One mmHg equals 133.322 Pa. The torr is essentially identical to mmHg and both units are accepted in specialised contexts.
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