PSI to mmHg Converter

PSI to mmHg

Convert psi (psi) to mmhg (mmHg). Both measure force per area, and the conversion comes up in weather, automotive, diving work.

The Formula

`` mmhg = psi × 51.7149252039 psi = mmhg × 0.0193367774595 `

One psi is 51.7149 mmhg, and one mmhg is 0.019337 psi.

Conversion Table

PSI	mmHg
1 psi	51.7149 mmHg
2 psi	103.4299 mmHg
5 psi	258.5746 mmHg
10 psi	517.1493 mmHg
25 psi	1,292.87 mmHg
50 psi	2,585.75 mmHg
100 psi	5,171.49 mmHg
500 psi	25,857.46 mmHg
1,000 psi	51,714.93 mmHg

The Other Direction

mmHg	PSI
1 mmHg	0.019337 psi
2 mmHg	0.038674 psi
5 mmHg	0.096684 psi
10 mmHg	0.193368 psi
25 mmHg	0.483419 psi
50 mmHg	0.966839 psi
100 mmHg	1.9337 psi
500 mmHg	9.6684 psi
1,000 mmHg	19.3368 psi

What Each Unit Is

PSI (psi) — pounds-force per square inch, equal to 6,894.76 pascals. The imperial pressure unit, still standard for US tyres, plumbing and compressed air.

mmHg (mmHg) — the pressure of a one-millimetre column of mercury, or 133.322 pascals. From the mercury barometer; medicine kept it after physics moved to pascals.

A Sense of Scale

• Car tyres run at 32–35 psi
• Household water is 40–60 psi
• Normal blood pressure is 120/80 mmHg
• Atmospheric pressure is 760 mmHg

Doing It in Your Head

Multiply by 51. That is off by 1.38% — close enough to judge a distance, a weight or a price, and not close enough to sign off on a drawing.

Exact	Mental shortcut
517.1493 mmHg	510 mmHg
5,171.49 mmHg	5,100 mmHg

Precision

The factor 51.7149252039 is rounded. For engineering work carry more digits than the table above, and round only at the end — rounding at each step compounds.

In Code

`javascript const psiToMmHg = (value) => value * 51.7149252039; ``

Where This Conversion Comes Up

• Weather
• Automotive
• Diving
• Aviation
• HVAC

How Many Decimals Do You Need?

Rounding the factor costs accuracy, and how much depends on the factor. Converting 137 psi with the factor truncated at each decimal place:

Decimals kept	Factor	137 psi becomes	Error
0	52	7,124	0.5512%
1	51.7	7,082.9	0.0289%
2	51.71	7,084.27	0.0095%
3	51.715	7,084.96	0.0001%
4	51.7149	7,084.94	—

A rule that holds for any conversion: round once, at the end. Rounding the factor and then multiplying compounds the error through every subsequent calculation, while carrying full precision and rounding the final answer does not.

The right number of significant figures is set by your input, not by the converter. If you measured psi to three significant figures, the answer in mmhg is only good to three — writing more digits claims precision the measurement never had.