Torr to Pascals Converter
Common Conversions
| torr | Pa |
|---|---|
| 0.001 | 0.1333 |
| 0.01 | 1.333 |
| 0.1 | 13.33 |
| 1 | 133.3 |
| 5 | 666.6 |
| 10 | 1333 |
| 50 | 6666 |
| 100 | 13332 |
| 200 | 26664 |
| 500 | 66661 |
| 760 | 101325 |
| 1000 | 133322 |
Why this conversion matters in chemistry
Vacuum gauges and surface-science instrumentation read in torr by long convention; SI-aligned facility records and physical-chemistry equations want pascals. The factor is 133.322 Pa per torr — close enough to the mmHg value to be interchangeable, since the torr is defined as exactly 1/760 of a standard atmosphere. An ultrahigh-vacuum chamber at 10⁻¹⁰ torr is 1.33 × 10⁻⁸ Pa, the value the SI-aligned data sheet would log even while the lab notebook stays in torr. Multiplying by 133.322 is the standard step that lets a vacuum reading meet a thermodynamic equation written in base SI throughout.
Formula
Where the factor comes from
Nothing needs deriving here in the ordinary sense, because 133.322368421… Pa is what a torr is. The standard atmosphere was fixed at exactly 101325 Pa; the torr was then defined as exactly one seven-hundred-and-sixtieth of that. A single division remains — 101325/760, reducing to 20265/152 — and it is exact and permanent, since neither input can drift. It is also endless: 152 factors as 2³ × 19, and the 19 pushes the decimal into an eighteen-digit repeating cycle instead of letting it stop. The pascal waiting at the far end is coherent SI, one newton per square meter, so a pressure expressed in pascals slots into kg·m⁻¹·s⁻² without further bookkeeping. That, rather than any gain in accuracy, is what the trip buys you.
Precision and significant figures
Multiplying by 133 inflates a short reading into a long one, and the extra length is decorative. A gauge showing 0.050 torr becomes 6.6661184 Pa; the two significant figures that went in are the two that come out. The factor being exact, it adds nothing to the uncertainty budget — the pascal figure carries the accuracy class of the gauge and nothing more. Where pascals genuinely hurt is at the extremes. At atmospheric scale the value runs to six digits with an ambiguous trailing zero or two, which is much of why kPa became the reporting convention; down in the ultrahigh-vacuum range it becomes an exponent, and exponents between −7 and −9 are where transcription errors hide best.
Worked Examples
One standard atmosphere — the calibration anchor in both unit systems.
Rotary-evaporator vacuum territory for many common solvents at moderate bath temperatures.
Schlenk-line working pressure for air-sensitive chemistry — the floor a rotary-vane oil pump can comfortably reach.
Water's vapor pressure at 25 °C — the value that goes into any calculation involving gas collected over water.
Common mistakes
Pascals converted, liters left alone
Converting to pascals is usually the first of two steps. R = 8.314 J/(mol·K) wants volume in cubic meters, not liters, so a gas-law calculation carrying P in Pa alongside V in L comes out a thousand-fold wrong. Reaching SI on the pressure side feels like the job is finished, and the volume sitting in a graduated cylinder never asks to be changed.
Writing kPa where you computed Pa
One torr is 133.322 Pa, which is 0.133322 kPa. Since most chemistry is reported in kilopascals, the habit of appending kPa to a pressure is strong enough to survive a calculation that actually produced pascals. The result still reads plausibly — 101 kPa and 101325 Pa are both familiar atmospheric numbers — so the slip usually surfaces only when something downstream refuses to balance.
Logged gauge values without their unit
Vacuum controllers let you pick the display unit from a menu, and torr, mbar and Pa all appear on the same readout in the same font. A number copied into a logbook without recording which unit was selected cannot be recovered later: 1.3 × 10⁻⁵ is three different pressures depending on the setting, spanning more than two orders of magnitude between them.