Atmospheric Pressure Converter
Convert atmospheric pressure between the units used in meteorology and aviation: hPa (hectopascals), mbar (millibars), inHg (inches of mercury), mmHg (millimeters of mercury), kPa, and atm.
Conversion Factors
1 atm = 101,325 Pa = 1013.25 hPa = 1013.25 mbar 1 atm = 760 mmHg = 760 Torr = 29.9213 inHg 1 atm = 14.6959 psi = 101.325 kPa
Unit Reference
| Unit | Definition | Where used |
|---|---|---|
| Pa (pascal) | 1 N/m² | SI reference |
| hPa (hectopascal) | 100 Pa = 1 mbar | Meteorology (most of world) |
| mbar (millibar) | 100 Pa = 1 hPa | Meteorology (traditional) |
| kPa (kilopascal) | 1000 Pa | Some weather reports, industry |
| atm (atmosphere) | 101,325 Pa exactly | Chemistry, diving |
| mmHg (millimeter of mercury) | 133.322387415 Pa | Medicine (blood pressure), vacuum |
| inHg (inch of mercury) | 3386.389 Pa | US aviation altimeter settings |
| psi (pound per square inch) | 6894.757 Pa | US engineering |
Worked Examples
Example 1: Standard atmospheric pressure
Standard atmospheric pressure is defined as exactly 101,325 Pa. This equals:
- 1013.25 hPa
- 1013.25 mbar
- 101.325 kPa
- 1 atm
- 760 mmHg
- 29.9213 inHg
- 14.6959 psi
Example 2: Weather report in hPa → inHg
A weather report gives 1020 hPa. To convert to inHg:
- 1020 hPa = 102,000 Pa.
- 102,000 ÷ 3386.389 = 30.121 inHg.
Result: 1020 hPa = 30.121 inHg.
Example 3: Aviation altimeter in inHg → hPa
An altimeter setting of 29.92 inHg converts to hPa:
- 29.92 × 3386.389 = 101,325 Pa.
- 101,325 ÷ 100 = 1013.25 hPa.
Result: 29.92 inHg = 1013.25 hPa.
Weather Pressure Patterns
| Condition | hPa / mbar | inHg |
|---|---|---|
| Strong high pressure | > 1030 | > 30.42 |
| Typical high pressure | 1020–1030 | 30.12–30.42 |
| Normal / standard | 1013.25 | 29.92 |
| Typical low pressure | 1000–1013 | 29.53–29.92 |
| Strong low / storm | < 990 | < 29.24 |
| Hurricane intensity | < 950 | < 28.05 |
| Record low (Typhoon Tip, 1979) | 870 | 25.69 |
Altitude and Pressure
Atmospheric pressure decreases with altitude. This relationship is used in aviation (altimeters) and mountain weather forecasts. Approximate values:
| Altitude | Pressure (hPa) |
|---|---|
| Sea level | 1013 |
| 1,000 m (3,281 ft) | 899 |
| 2,000 m (6,562 ft) | 795 |
| 3,000 m (9,843 ft) | 701 |
| 5,500 m (18,000 ft) | 500 |
| 8,848 m (Everest summit) | 337 |
| 10,700 m (35,000 ft, jet cruise) | 238 |
Real-World Uses
- Weather forecasting: High-pressure systems bring clear weather; low-pressure systems bring clouds and precipitation. Pressure is reported in hPa/mbar worldwide and inHg in the US.
- Aviation altimeter: Pilots set the altimeter to the local pressure (QNH) reported in inHg (US) or hPa (international) to know their actual altitude.
- Diving: Pressure increases with depth. Divers use atm for depth calculations.
- Medical: Blood pressure is measured in mmHg; ventilator settings use cmH₂O, hPa, or kPa.
- Industrial: Vacuum systems use mmHg or Torr; HVAC systems use inHg or kPa.
Related Converters
- Pressure Converter (hub)
- mmHg to kPa
- Atmospheres to Pascals
- Altitude Converter
- All Geography Converters
Frequently Asked Questions
What is standard atmospheric pressure?
Standard atmospheric pressure is 101,325 Pa = 1013.25 hPa = 1013.25 mbar = 1 atm = 760 mmHg = 29.9213 inHg.
How do you convert hPa to inHg?
Multiply by 0.02953. For example, 1020 hPa × 0.02953 = 30.12 inHg. More precisely, divide by 33.86389.
Why does the US use inHg for pressure?
US customary tradition: mercury barometers were standard for measuring atmospheric pressure, and the inch of mercury was a practical unit at US latitudes. It persists in aviation weather reports.
What pressure does a hurricane have?
Hurricane intensity is categorized by wind speed, but strong hurricanes can have very low central pressure — typically below 950 hPa (28.05 inHg). The record low was Typhoon Tip in 1979 at 870 hPa (25.69 inHg).
What is the difference between hPa and mbar?
They are the same value. 1 hPa = 1 mbar = 100 Pa exactly. Meteorologists use both interchangeably, with hPa now standard in most countries.