How many mmHg is 1 inHg?

1 inch of mercury (inHg) equals exactly 25.4 millimeters of mercury (mmHg). This is because 1 inch = 25.4 mm by definition, and both units measure pressure via the same mercury column height, so the conversion is exact.

How do I convert inHg to mmHg manually?

Multiply the inHg value by 25.4. For example, 29.92 inHg × 25.4 = 759.97 mmHg, which is essentially standard atmospheric pressure. To convert mmHg back to inHg, divide by 25.4.

What is standard atmospheric pressure in inHg and mmHg?

Standard atmospheric pressure is 29.9213 inHg, which equals 760.00 mmHg (also written as 760 Torr at 0 °C). US weather and aviation services use 29.92 inHg as the conventional reference for pressure altitude.

Is mmHg the same as Torr?

For practical purposes, 1 mmHg ≈ 1 Torr. Strictly, 1 Torr = 1/760 standard atmosphere = 133.322 Pa, while 1 mmHg is defined via mercury density at 0 °C = 133.3224 Pa — a difference of less than 0.0002%, negligible for most applications.

Why does the US use inHg for weather while most countries use mmHg or hPa?

The United States adopted inHg for aviation altimeters and domestic weather broadcasts before metric standardization. Most other countries use hectopascals (hPa) or millibars for weather and mmHg for medical blood pressure. Use this converter when your data source gives inHg but you need mmHg.

What is 29.92 inHg in mmHg?

29.92 inHg × 25.4 = 759.97 mmHg, essentially standard atmospheric pressure (760 mmHg). US weather services cite 29.92 inHg as the standard sea-level reference for pressure altitude calculations.

inHg to mmHg Converter

Name: inHg to mmHg Converter
Availability: InStock
Author: Nham Vu

Enter a pressure in inHg and get the mmHg equivalent instantly, with reverse mmHg-to-inHg conversion and a reference table.

Converter

Pressure in inches of mercury (inHg)

= — mmHg

Reverse: millimeters of mercury (mmHg)

= — inHg

Reference Table

inHg	mmHg	Context
1.00	25.40	Unit definition
10.00	254.00	~1/3 atm
20.00	508.00	High altitude ref.
29.92	759.97	US standard sea level
29.9213	760.00	1 atm (exact)
30.00	762.00	Common weather ref.
31.00	787.40	High pressure system
100.00	2,540.00	Industrial range

Formula: mmHg = inHg × 25.4 | inHg = mmHg ÷ 25.4

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Summary

Enter a pressure in inHg and get the mmHg equivalent instantly, with reverse mmHg-to-inHg conversion and a reference table.

How it works

Enter the pressure value in inches of mercury (inHg) in the top input.
The mmHg result appears instantly without pressing any button.
Use the reverse field to convert mmHg back to inHg.
Click "Copy" next to any result to copy the value to your clipboard.
Check the reference table for common inHg-to-mmHg conversions at a glance.

Use cases

Convert US aviation altimeter settings (inHg) to mmHg for international instruments.
Translate weather station barometric pressure from inHg to mmHg for metric-system reports.
Cross-reference blood pressure measurements when switching between inHg and mmHg units.
Convert vacuum gauge readings between inHg and mmHg in industrial or HVAC applications.
Verify pressure thresholds in pneumatic systems that mix inHg and mmHg specifications.
Look up standard sea-level pressure equivalences for meteorology or aviation calculations.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu