kPa to Torr Converter
Common Conversions
| kPa | torr |
|---|---|
| 0.1 | 0.75 |
| 1 | 7.501 |
| 5 | 37.503 |
| 10 | 75.006 |
| 25 | 187.516 |
| 50 | 375.031 |
| 100 | 750.062 |
| 101.325 | 760 |
| 150 | 1125.093 |
| 200 | 1500.124 |
| 500 | 3750.31 |
Why this conversion matters in chemistry
Older Antoine-equation tables list vapor pressures in torr; modern NIST WebBook data lists the same quantities in kPa. Water at 25 °C has a vapor pressure of 3.17 kPa, equivalently 23.8 torr — the bridging value that lets a contemporary lab cross-check a measurement against the pre-SI literature. The constant of 7.50062 torr per kPa comes from 760 torr = 101.325 kPa, the historical definition of standard atmospheric pressure. It comes up when modern SI vapor-pressure data needs to land alongside legacy torr-based references or vacuum-gauge readings.
Formula
Where the factor comes from
One of these units was built up and the other was cut down. The pascal is assembled out of mechanics — a newton spread over a square meter — and the kilopascal is that with a prefix attached. The torr was made by taking the standard atmosphere, already fixed at exactly 101325 Pa, and slicing it into 760 equal parts, so 1 torr = 101325/760 Pa = 133.32236842… Pa. Dividing 1000 Pa by that yields the exact fraction 30400/4053, or 7.500616827… torr per kilopascal. Both defining statements are declarations, so the factor carries no experimental uncertainty; but 4053 divides no power of ten, so the decimal runs on and every printed version of it is a truncation somebody chose.
Precision and significant figures
Truncating the factor is safe long before the instrument becomes the limit. 7.50062 holds the exact ratio to four parts in ten million, and even a flat 7.5 is off by 0.008 percent, under a tenth of a torr across a whole atmosphere. What is not safe is letting the larger number invent resolution: a gauge showing 1.2 kPa carries two figures, so 9.0 torr is the answer and 9.001 is decoration. The mismatch runs the other way in rough vacuum, where a controller displaying whole torr quantises in steps of 0.133 kPa — a coarseness that the extra decimal places of the kilopascal form conceal rather than remove.
Worked Examples
Standard atmospheric pressure expressed in both unit systems.
The conversion anchor — useful for any quick mental scale check.
Water vapor pressure at 25 °C — the value behind any humid-air calculation.
Exactly 1 bar — IUPAC standard pressure expressed in torr.
Common mistakes
Forward and reverse shortcuts do not match
Multiplying by 7.5 and dividing by 0.133 are both convenient, and they are not inverses: 7.5 × 0.133 = 0.9975, so a value converted out and back sheds a quarter of a percent each round trip. Pair 7.5 with a division by 7.5, or 7.50062 with 0.1333224, but never a rounded factor in one direction against a differently rounded one in the other.
Residual gas analyzer partial pressures are relative
An RGA reports each species as a partial pressure in torr, but those figures depend on ionization cross-section and detector response, which differ from gas to gas. Summing them and converting to kilopascals produces a total that need not agree with the chamber gauge. Treat individual torr values as relative unless the instrument has been calibrated for the species you are actually looking at.
The thermodynamic standard state is 750.062 torr
Equilibrium constants come out dimensionless because every pressure is divided by the standard state, and since 1982 that state has been 1 bar — 750.062 torr, not 760. Build a Kp from torr partial pressures and divide by 760 and each term shifts by 1.3 percent, which raising to a stoichiometric coefficient then compounds. Convert, reference to the standard state, and only then take the logarithm.