Pascal to Torr Converter
Common Conversions
| Pa | torr |
|---|---|
| 1 | 0.007501 |
| 10 | 0.075006 |
| 100 | 0.750062 |
| 133.322 | 1 |
| 500 | 3.75 |
| 1000 | 7.501 |
| 5000 | 37.503 |
| 10000 | 75.006 |
| 50000 | 375.031 |
| 100000 | 750.062 |
| 101325 | 760 |
| 200000 | 1500.12 |
Why this conversion matters in chemistry
Pascal is the SI unit and the one most modern equipment specs are written in; torr is what working chemists still reach for when they talk about vacuum, especially in the low-pressure regime. A mass spectrometer ion source running at 2 × 10⁻³ Pa sits at 1.5 × 10⁻⁵ torr — same pressure, two different ways to write it. The conversion factor drops cleanly out of the atmospheric pressure equivalence: 1 atm is 760 torr and 101,325 Pa, so 1 torr is 133.322 Pa. Multiplying pascals by 0.007501 is the forward direction. Most of the time you're converting because a datasheet and a lab notebook use different conventions and you need them to agree.
Formula
Where the factor comes from
The torr is pinned to the atmosphere rather than to mercury: it is exactly 1/760 of a standard atmosphere, so 101325 ÷ 760 = 133.32236842… Pa and the forward factor is the reciprocal, 760/101325 = 0.0075006168… Both endpoints are defined integers, which makes the ratio exact as a fraction even though the decimal never closes. Worth keeping separate in your head is the conventional millimeter of mercury, a different construction entirely — a fixed mercury density of 13595.1 kg/m³ under standard gravity, giving 133.322387415 Pa. That sits about 1.4 parts in 10⁷ above the torr. The two were built to coincide and for every practical purpose they do, but they are not the same definition and a metrology lab treats them separately.
Precision and significant figures
Six figures of the factor, 0.00750062, land within half a part per million of exact; the 0.007501 in wide circulation is high by 51 ppm, still invisible against any gauge. Vacuum instrumentation sets the real limit, and it varies wildly across the range — capacitance manometers are commonly specified to a fraction of a percent of reading, while thermal-conductivity and hot-cathode gauges are often quoted in tens of percent over parts of their span. Down in the fine-vacuum region the exponent matters far more than any digit of the factor: 1 × 10⁻³ Pa is 7.5 × 10⁻⁶ torr, and a misplaced decade does damage that no amount of rounding care could offset.
Worked Examples
Sea-level atmospheric pressure. The anchor equivalence the factor is derived from.
The base conversion — 1 torr is defined as exactly 1/760 of a standard atmosphere, which works out to 133.322 Pa.
A low vacuum reading — the kind of pressure a basic water aspirator or diaphragm pump can pull.
Moderate vacuum, roughly where a rotary evaporator sits when pulling a low-BP solvent at reasonable bath temperatures.
Common mistakes
Millitorr and "microns" are one unit
Rough-vacuum work is spoken in microns, meaning microns of mercury, and one micron is one millitorr. Convert 13.3 Pa and you get 0.1 torr — the same pressure a technician would call 100 microns. Reading a torr figure onto a gauge graduated in microns, or the reverse, is a clean factor of a thousand with nothing in the units to flag it.
Most vacuum gauges are calibrated for nitrogen
Pirani and ionization gauges infer pressure from a gas-dependent property and are normally calibrated against nitrogen or dry air. With solvent vapor in the line the displayed pascal value is not the true pressure, and converting it to torr carries that species error straight through. The arithmetic is exact; the number going into it may not be.
Multiply by 0.0075, divide by 133.322
Both numbers appear on this page and only one belongs in each direction. Divide 1000 Pa by 0.0075006 and you get 133,300 instead of 7.5 — wrong by a factor near 18,000, yet still looking like a plausible pressure in some unit. The check is directional and never fails: the torr figure is always the smaller of the two, by roughly 133.