Torr to Millibar Converter
Common Conversions
| torr | mbar |
|---|---|
| 0.01 | 0.01333 |
| 0.1 | 0.13332 |
| 0.25 | 0.33331 |
| 0.5 | 0.66661 |
| 1 | 1.33322 |
| 2 | 2.66645 |
| 5 | 6.66612 |
| 10 | 13.332 |
| 25 | 33.331 |
| 50 | 66.661 |
| 100 | 133.322 |
| 1000 | 1333.22 |
Why this conversion matters in chemistry
Transferring a sputter-deposition recipe between continents is the kind of thing that lands on this conversion. A 5 mTorr argon process pressure on a US thin-film tool needs to come up as 6.7 × 10⁻³ mbar on the mass-flow controller of a European-built instrument running the same published recipe. The factor 1.33322 mbar/torr traces straight back to 1 torr = 101325/760 Pa = 133.32 Pa, then rescaled. So this is the bookkeeping that lets a torr-graduated manometer and a digital mbar transducer agree on the same vacuum.
Formula
Where the factor comes from
Multiply by 1.333 often enough and the factor starts to look like 4/3. It isn't. Both ends of this conversion are pinned to exact pascal counts: the bar was fixed at 10⁵ Pa, which makes a millibar exactly 100 Pa, and the torr at exactly one seven-hundred-and-sixtieth of the 101325 Pa standard atmosphere. Dividing one by the other gives 101325 ÷ 76000, reducing to 4053/3040 = 1.333223684210526… Two exact anchors make the factor itself exact, but the 19 buried in 3040 keeps the decimal from terminating — it repeats on an eighteen-digit cycle. The naive 4/3 runs about 82 parts per million high, invisible on any gauge, though that near-miss is an accident of where the barometer happened to stand rather than anything the two definitions share.
Precision and significant figures
A factor this close to one moves significant figures across almost unchanged: three digits of torr give three digits of millibar and no more. What the multiplication supplies is a tail — a gauge showing 10 torr produces 13.3322368 mbar — and transcribing that tail manufactures seven digits from two. The factor being exact, it never limits anything; the gauge always does. Millibar controllers compound the problem by displaying a fixed number of decimals, so round torr values arrive as awkward millibar values and get rounded again at the panel. A reading of 20.0 mbar on such a display pins the true pressure only to within about 0.04 torr either way.
Worked Examples
Standard atmospheric pressure — the anchor.
One torr — about a typical small vacuum increment.
About a high vacuum for sublimation work.
About a moderate rotary-evaporator vacuum.
Common mistakes
Gauge-referenced mbar has a different zero
Plenty of industrial transducers report millibar relative to ambient rather than to vacuum, so their zero sits near 1013 mbar absolute. A torr value converted for one of those channels has to be offset by local barometric pressure first, not merely scaled by 1.333. The labels that distinguish the two, mbar a and mbar g, are small on the datasheet and absent from the display.
Literature torr pressures into an mbar rotovap
Reduced-pressure boiling points in the older organic literature are almost always quoted in torr, while the vacuum controller on a modern rotary evaporator is denominated in millibar. Typing a published 15 into a millibar field asks for 11.3 torr rather than 15 torr — a deeper vacuum than the procedure intended, and enough to drop the head temperature and carry distillate over early.
hPa on a readout is already millibar
Barometric and meteorological data arrive in hectopascals, and 1 hPa is exactly 1 mbar — same number, different name. Converting torr to millibar and then applying some further factor to reach hPa scales the result twice. The reverse catches people too: an hPa figure quoted alongside torr looks like it still needs work when it needs none at all.