Pascals to mmHg Converter
Common Conversions
| Pa | mmHg |
|---|---|
| 10 | 0.075 |
| 100 | 0.75 |
| 133.322 | 1 |
| 1000 | 7.501 |
| 5000 | 37.503 |
| 10000 | 75.006 |
| 50000 | 375.031 |
| 100000 | 750.062 |
| 101325 | 760 |
| 200000 | 1500.124 |
| 500000 | 3750.31 |
Why this conversion matters in chemistry
Tonometry is the case where this gets clinical fast. Newer intraocular-pressure devices log in pascals under the hood while the ophthalmologist still reads mmHg on the dashboard — Goldmann reference units. A 2000 Pa reading equals 15.0 mmHg, which sits right at the upper normal boundary; that's where a single decimal place in the conversion drives the call to either re-measure or open a glaucoma workup. The factor 0.0075006 traces back to 1 mmHg = 133.322 Pa, itself the product of mercury's density and standard gravity acting over one millimeter.
Formula
Where the factor comes from
Read this direction as a question about a fluid rather than a change of label: how tall a mercury column would this pressure hold up? Rearranging p = ρgh gives h = p/(ρg), and the answer emerges as a length only because a density and a gravity were fixed beforehand — 13595.1 kg/m³ and 9.80665 m/s², both assigned by convention rather than measured on the day. Their product is 133.322387415 Pa per millimeter, so 1 Pa = 0.0075006158 mmHg. The reciprocal is where rounding first appears: the defining number terminates, its inverse does not. Route through the torr instead, dividing by 101325/760, and you get 0.0075006168 — a difference in the eighth figure that no barometer will resolve.
Precision and significant figures
Nothing this factor gets used for needs more than 0.0075006. Rounding to a flat 0.0075 costs 0.008 percent, which moves a converted atmospheric reading by about 0.06 mmHg: invisible on a bench manometer, visible on a precision barometer, and worth knowing which one you are holding. Figures in the result belong to the pascal reading rather than to the factor. A transmitter specified at a tenth of a percent of a 100 kPa span is uncertain by 100 Pa — three quarters of a millimeter of mercury — so a display showing 750.06 mmHg is honest to about 750.1 and no further.
Worked Examples
Standard atmospheric pressure expressed in both unit systems.
Exactly one mmHg in pascals — the conversion anchor in reverse.
Vapor pressure of water at 25 °C — the value behind humid-air calculations.
Exactly 1 bar in mmHg — the IUPAC reference pressure.
Common mistakes
The mercury column here is imaginary
Converting a pascal reading into mmHg puts no mercury anywhere near the experiment. The number is a defined equivalence, so the corrections belonging to a real column — fluid temperature, expansion of the scale, capillary depression at the meniscus — have no business being applied to it. Those corrections live upstream, on instruments that actually contain mercury.
Vacuum dials measure depression, not pressure
Many are graduated as vacuum below ambient rather than as absolute pressure, so a reading of 700 mmHg vacuum corresponds to roughly 60 mmHg absolute — nearly an atmosphere away from the literal number on the face. A value converted from pascals is absolute by construction, so it has to be subtracted from ambient before it can be set against such a dial.
Water manometers do not use this factor
One pascal is 0.0075 mm of mercury but 0.102 mm of water, a ratio of 13.6 set entirely by the two densities. Low-pressure lines often carry water or oil manometers precisely because the column travels further per pascal, and applying the mercury factor to a fluid that is not mercury misreads the pressure by more than an order of magnitude.