Convert Inches of Mercury to Millibars
Inch of Mercury (inHg) to Millibar (mbar) unit conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 inHg = 33.8638 mbar
1 Inch of Mercury = 33.8638 Millibars
1 Millibar = 0.029530059 Inches of Mercury
1 inHg in every supported unit
Conversion chart: Inch of Mercury to Millibars
Conversion table
| Inch of Mercury (inHg) | Millibar (mbar) |
|---|---|
| 0.01 inHg | 0.338638 mbar |
| 0.1 inHg | 3.38638 mbar |
| 1 inHg | 33.8638 mbar |
| 2 inHg | 67.7276 mbar |
| 3 inHg | 101.5914 mbar |
| 5 inHg | 169.319 mbar |
| 10 inHg | 338.638 mbar |
| 20 inHg | 677.276 mbar |
| 50 inHg | 1693.19 mbar |
| 100 inHg | 3386.38 mbar |
| 1000 inHg | 33863.8 mbar |
Inch of Mercury (inHg)
Definition: The pressure exerted by a column of mercury one inch tall under standard gravity, a direct manometer-based unit of measurement.
History: Developed alongside early mercury barometers in the 17th and 18th centuries, when pressure was measured directly by the height of mercury it could support inside a sealed glass tube.
Current use: Used in United States weather reports for barometric pressure and in aviation altimeter settings, where pilots dial in the local pressure reading in inches of mercury.
Millibar (mbar)
Definition: One-thousandth of a bar, exactly equal to one hectopascal.
History: Adopted early in the 20th century alongside the bar itself as a practically sized subdivision for measuring the relatively small pressure variations that drive weather systems.
Current use: Still the standard unit for reporting barometric pressure and hurricane intensity in United States weather forecasts, even as most of the world has shifted to the equivalent hectopascal.
Supported Units
| Unit | Symbol | In Pascals |
|---|---|---|
| Pascal | Pa | 1 Pa |
| Kilopascal | kPa | 1000 Pa |
| Megapascal | MPa | 1000000 Pa |
| Hectopascal | hPa | 100 Pa |
| Bar | bar | 100000 Pa |
| Millibar | mbar | 100 Pa |
| Pound per Square Inch | psi | 6894.7573 Pa |
| Standard Atmosphere | atm | 101325 Pa |
| Torr | Torr | 133.32237 Pa |
| Inch of Mercury | inHg | 3386.38 Pa |
About These Parameters
- Value
- The pressure reading you want to convert, expressed in the "From" unit. Accepts decimals.
- From Unit
- The pressure scale your input value is currently measured in — for example, PSI on a US tire gauge or hectopascals on a weather report.
- To Unit
- The pressure scale you want the result converted into. Use the swap button to flip From and To instantly.
How Pressure Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to the pascal. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Inch of Mercury → Millibar: multiply by 33.8638. For example, 1 inHg × 33.8638 = 33.8638 mbar.
SI vs. Customary Units
The metric units on this page — pascal, kilopascal, megapascal, hectopascal, bar, and millibar — all scale by powers of ten, so converting between them is just moving a decimal point. PSI is a US customary unit built from pounds-force and square inches, unrelated to the metric scale, while torr and inches of mercury are older manometer-based units defined by the height of a mercury column a pressure could support — each needs its own precise multiplier rather than a round decimal shift.
Why Atmospheric Pressure Matters
Standard atmospheric pressure — 101,325 Pa, or 1 atm — is the reference point most pressure units are built around, because it is the pressure every person and machine on Earth's surface experiences by default. Meteorologists track small deviations from this baseline, measured in hectopascals or millibars, to forecast weather: a falling barometer reading signals an approaching low-pressure system and possible storms, while a rising one signals clear, stable conditions.
Example
1 inHg equals 33.8638 mbar. For scale, that's about 0.03× standard atmospheric pressure (1 atm, or 29.921332 inHg) — roughly the pressure difference a typical car tire holds above the surrounding air (about 32 psi, or 2.2 bar).
Frequently Asked Questions
How many Millibars are in 1 Inch of Mercury?
1 Inch of Mercury (inHg) equals exactly 33.8638 Millibars (mbar).
Why do US tire gauges use PSI?
The United States never mandated metrication, so pounds and inches stayed the default units for everyday measurement, including the pound-force-per-square-inch pressure scale used on tire gauges, plumbing fixtures, and compressed air tools. Most of the rest of the world reads the same measurement in bar or kilopascals.
What's the difference between a bar and an atmosphere?
A bar is a round metric unit equal to exactly 100,000 pascals, chosen for convenient arithmetic; a standard atmosphere is fixed at exactly 101,325 pascals, the measured average air pressure at sea level. The two are close — 1 atm is about 1.01325 bar — but they are defined differently and are not interchangeable in precise scientific work.
How accurate are these conversions?
Every conversion factor used here is the exact, internationally standardized value (e.g. 1 atm = exactly 101,325 Pa, and 1 psi = exactly 6,894.7572931783 Pa) — results are limited only by floating-point display precision, not by rounded conversion constants.