Pressure Converter
Convert a pressure value between Pa, kPa, MPa, bar, atm, mmHg, cmHg, inHg, psi, and torr. Enter the value and select the starting and target units.
Convert Pressure Between Units
Pressure Conversion Formula
Where:
- \(P_{\text{from}}\) — pressure value in the starting unit
- \(P_{\text{to}}\) — pressure value in the target unit
- \(f_{\text{from}}\) — pascals per starting unit
- \(f_{\text{to}}\) — pascals per target unit
The converter first expresses the entered value in pascals, then divides by the number of pascals in one target unit. This changes the unit without changing the pressure represented.
Pressure – Calculation Example
Example: convert the default value of 101,325 Pa to atmospheres (atm).
\[101{,}325\ \text{Pa}\times\frac{1\ \text{Pa/Pa}}{101{,}325\ \text{Pa/atm}}=1\ \text{atm}\]
Result: 101,325 Pa = 1 atm.
How to use the calculator
- Enter the number you want to convert in Pressure value. The field accepts zero or a positive value.
- Choose the unit of that number under From unit.
- Choose the unit you need under To unit. You can select any of the listed units, including the same unit as your starting value.
- Read Converted Pressure. The result includes the target unit and is rounded to no more than 10 decimal places.
What pressure units measure
Pressure describes force distributed over an area: \(P=F/A\). The pascal (Pa), the SI unit of pressure, equals one newton per square meter. A larger pressure means more force acts on each unit of area. If you need to convert a force separately, use the force converter; converting pressure alone does not tell you the total force unless the area is known.
Different fields use different pressure units. Kilopascals and megapascals keep large values manageable in engineering calculations; bar and psi are common on equipment specifications. Atmospheres provide a reference based on standard atmospheric pressure: exactly 101,325 Pa per atm. This is a defined reference value, not a claim that local air pressure is always 1 atm.
Mercury-column units appear in weather reports, aviation, vacuum measurements, and blood pressure readings. Millimeters of mercury (mmHg), centimeters of mercury (cmHg), inches of mercury (inHg), and torr are available here. For example, a measurement reported in mmHg can be converted to kPa for comparison with a specification expressed in SI units. Pressure units also matter in gas-solubility calculations; see the Henry’s Law calculator when pressure is one of the inputs to that relationship.
Conversion factors used
Each factor below is the number of pascals in one unit. The calculator multiplies by the factor for From unit and divides by the factor for To unit.
| Unit | Pascals per unit |
|---|---|
| Pa | 1 |
| kPa | 1,000 |
| MPa | 1,000,000 |
| bar | 100,000 |
| atm | 101,325 |
| mmHg | 133.322368 |
| cmHg | 1,333.22368 |
| inHg | 3,386.389 |
| psi | 6,894.757 |
| torr | 133.322368 |
For a quick sense check, 100 kPa equals 1 bar, while 1 atm is slightly higher at 101.325 kPa. Converting in the reverse direction uses the same factors: 1 bar ÷ 101,325 Pa per atm, after expressing 1 bar as 100,000 Pa, gives approximately 0.9869232667 atm.
Assumptions and practical limits
This is a unit converter, not a pressure sensor or a calculator for how pressure changes with height, temperature, or flow. It applies fixed factors to the value you enter. In particular, it does not distinguish absolute pressure from gauge pressure. Both can use the same units, but a gauge reading is relative to its reference pressure. If you need to change between gauge and absolute pressure, account for that reference separately before or after converting units.
The calculator uses the same factor for mmHg and torr, so it returns identical values for those units. Definitions and measurement conventions can differ slightly in high-precision work; the listed factors determine this calculator’s results. Likewise, psi and inHg use the rounded factors shown above. Check the required convention if you are working to a tighter tolerance than those factors allow.
The input does not accept negative values. Zero is valid, but its physical meaning depends on whether the original reading is absolute or gauge pressure. For very small converted values, the display’s rounding to 10 decimal places may hide additional nonzero digits; keep that display limit in mind when comparing tiny pressures.
Frequently Asked Questions
How do I convert psi to bar by hand?
Multiply the psi value by approximately 0.06895. For example, 30 psi is about 2.07 bar. To check the direction of your calculation, remember that one bar is roughly 14.5 psi, so a value expressed in bar should be smaller than the same pressure expressed in psi.
What is normal atmospheric pressure in different units?
Standard atmospheric pressure is 101.325 kPa, or about 1.01325 bar, 14.7 psi, and 760 mmHg. These are reference values, not a single normal reading for every location. Actual air pressure changes with weather and elevation, so a local measurement can differ without indicating a problem.
How do I convert a tire pressure reading to absolute pressure?
Most tire gauges report gauge pressure, which is measured relative to the surrounding air. Add local atmospheric pressure to obtain absolute pressure, then convert units if needed. For example, a reading of 30 psi gauge is about 44.7 psi absolute if the surrounding pressure is 14.7 psi. Use the actual local atmospheric pressure when accuracy matters.
How do I convert a weather report from hPa to kPa or inHg?
One hectopascal (hPa) equals 100 Pa, or 0.1 kPa. If your weather report says 1,010 hPa, enter 101 kPa to convert it to inHg or another available unit. This avoids treating hPa as Pa—a mistake that would make the converted pressure 100 times too small.
How do I convert blood pressure from mmHg to kPa?
Convert the two readings separately. For example, 120/80 mmHg is approximately 16.0/10.7 kPa, with the systolic value first and the diastolic value second. Changing units does not change what the reading means clinically. If you are concerned about a blood pressure result, discuss it with a healthcare professional.
Can I convert a negative gauge pressure or vacuum reading?
Not directly: this calculator accepts only zero or positive inputs. A negative gauge reading means the pressure is below its reference pressure, not that absolute pressure is negative. For example, at 14.7 psi atmospheric pressure, −5 psi gauge is 9.7 psi absolute. Convert that positive absolute value, and label the result as absolute pressure.
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