Convert pressure between PSI and mmHg with adjustable decimal places, reverse conversion, and a clear note about the standard mmHg convention.
Table of contents
How to use our PSI to mmHg Converter
- Choose Convert to pick your starting unit: PSI to mmHg or mmHg to PSI.
- Enter your number in Value to convert. You can type commas or a negative sign if you are working with a signed pressure difference.
- Pick Decimal places to control how many digits appear in Converted pressure and the Quick reference table.
- Click Calculate to see Converted pressure, Conversion factor used, Formula used, and the note about mmHg.
- Sanity-check the answer by making sure the unit direction matches your choice and that converting 1 PSI gives about 51.7149 mmHg, while 760 mmHg gives about 14.696 PSI.
Definitions
PSI: Pounds per square inch, a pressure unit commonly used for tires, air systems, and other US measurements [2].
mmHg: Millimeters of mercury, a pressure unit often seen in medicine and lab work. In this converter, it follows the standard mmHg at 0 C table convention.
Converted pressure: The pressure value after changing from the starting unit to the other unit.
Conversion factor used: The number multiplied by your starting value to get the target unit.
Formula used: The exact multiply rule the converter applies for the chosen direction.
Decimal places: How many digits show after the decimal point in the displayed result and quick table.
Common mistakes and quick fixes
Mistake: Typing a value in Value to convert but forgetting to switch Convert to the right direction.
Fix: Check whether your starting number is in PSI or mmHg, then pick the matching Convert option before you calculate.
Mistake: Leaving Value to convert blank or entering text that is not a real number.
Fix: Enter a numeric value in Value to convert . Commas and spaces are fine, but words are not.
Mistake: Reading Converted pressure as if it kept the same unit as the input.
Fix: The Converted pressure unit always changes to the other unit based on the Convert choice.
Mistake: Using too few digits in Decimal places for school work, calibration notes, or repeated conversions.
Fix: Increase Decimal places to 4 or 6 if you need a more precise displayed result.
Mistake: Treating PSI in this tool as if it automatically changes gauge pressure to absolute pressure.
Fix: Use Converted pressure only for unit conversion. The pressure reference itself does not change just because the unit changes.
Mistake: Assuming the Note about mmHg means mmHg and Torr are exactly the same in every context.
Fix: Use the converter's stated mmHg convention and do not swap in Torr unless your class, lab, or device specifically says to do that.
Limitations & Key Assumptions / Boundary Conditions
- This tool converts units only. It does not change gauge, absolute, or differential pressure reference.
- mmHg is treated with the standard pressure-table convention of mmHg at 0 C, so values may differ slightly from definitions used in other specialized contexts.
- Displayed results depend on the selected Decimal places; the shown number is rounded for display.
- Negative inputs are allowed because some pressure differences are signed, so a negative converted value can be valid.
- The reverse factor is a rounded reciprocal for practical use, so tiny display differences can appear if you round heavily and convert back and forth.
- This converter does not treat mmHg and Torr as exactly identical units.
Methodology
Calculation method
The converter uses one multiplication factor based on the selected direction.
mmHg = psi x 51.714918
psi = mmHg x 0.01933678
These are standard pressure conversion factors used for PSI and mmHg tables, with mmHg treated as mmHg at 0 C [1]. PSI is pounds per square inch [2].
How the result is shown
After the raw conversion is calculated, the displayed Converted pressure is rounded to the selected Decimal places. The same rounding choice is used in the Quick reference table, but the underlying conversion step still uses the fixed factor above.
Mini example
If Convert is set to PSI to mmHg and Value to convert is 1, multiply 1 by 51.714918.
1 x 51.714918 = 51.714918 mmHg
With 4 decimal places, the displayed Converted pressure is 51.7149 mmHg.
If Convert is set to mmHg to PSI and Value to convert is 760, multiply 760 by 0.01933678.
760 x 0.01933678 = 14.6960 psi
Assumptions and calculation choices
The tool strips commas and spaces before reading the number, allows negative values, and blocks blank or non-numeric entries with an error. It is a unit converter only, so it does not adjust for whether your original reading is psig, psia, or another reference condition.