How many Millibars (mbar) to 1 Inch of Mercury (inHg)

The story behind the answer

33.9 is correct because 1 inch of mercury (inHg) corresponds to about 33.86 millibars (mbar). You can see this from the standard atmospheric pressure: 1 atm = 29.92 inHg = 1013.25 mbar, so 1 inHg = 1013.25 ÷ 29.92 ≈ 33.86 mbar, rounded to 33.9. (Note: 1 mbar = 1 hPa.)

Context tip: inHg comes from mercury barometers, where pressure is measured by the height of a mercury column (P = ρgh). Meteorologists often switch between inHg and mbar. A handy memory hook: “Three-three-nine” — 1 inHg ≈ 33.9 mbar, and “about 30 inches ≈ 1013 mbar” (standard sea-level pressure). If you remember 30 ↔ 1013, dividing gives you ≈34 mbar per inch.