Poise to Pascal-Seconds Viscosity Converter
Common Conversions
| P | Pa·s |
|---|---|
| 0.01 | 0.001 |
| 0.05 | 0.005 |
| 0.1 | 0.01 |
| 0.5 | 0.05 |
| 1 | 0.1 |
| 2 | 0.2 |
| 5 | 0.5 |
| 10 | 1 |
| 50 | 5 |
| 100 | 10 |
Why this conversion matters in chemistry
Cross-era rheology data digitization hits this regularly. Glycerol at 20 °C reported as 14.9 P in rheology archives from the mid-20th century is 1.49 Pa·s in modern SI form — the value entered when porting a legacy Ferry or Markovitz dataset for comparison against a modern cone-plate measurement. The ratio of 0.1 Pa·s per P comes from the CGS gram-centimeter (1 P = 1 g/(cm·s)) versus SI kilogram-meter (1 Pa·s = 1 kg/(m·s)) base-unit difference. In practice it's a unit handoff between legacy fluid-dynamics literature and SI-aligned modern publications.
Formula
Where the factor comes from
One gram per centimeter-second, rewritten in kilograms and metres: 10⁻³ kg divided by 10⁻² m and by a second gives 10⁻¹ kg·m⁻¹·s⁻¹, which is 0.1 Pa·s. That is the entire derivation, and its tidiness is not typical of the CGS inheritance — the mechanical units generally land on clean powers of ten, while the CGS electromagnetic units do nothing of the sort. Since 2019 the kilogram has been defined through a fixed value of the Planck constant, but that redefinition changed how the unit is realised, not how the gram relates to it; decimal prefixes are definitions and always were. So the 0.1 is exact, and a converted legacy viscosity is no less certain than the figure the original author wrote down.
Precision and significant figures
The factor contributes nothing, so the entire question is what the source value was worth. Poise-denominated data generally comes from older compilations or from points lifted off a published graph, and two or three significant figures is a generous reading of either. 14.9 P becoming 1.49 Pa·s is honest; 1.490 is not. Older sources are also looser about stating conditions, and for a liquid the temperature governs more than any digit — a couple of percent per kelvin near room temperature is ordinary. Where the original gives a temperature only to the nearest degree, that alone caps the converted value at roughly three figures no matter how the arithmetic comes out.
Worked Examples
Water at 20 °C — equivalently 1 cP, the canonical anchor.
About a moderately viscous liquid.
Glycerol at 25 °C — useful as a high-viscosity reference.
Common mistakes
Gas viscosities are tabulated in micropoise
Gases sit orders of magnitude below liquids, so their viscosities are printed in micropoise — air near room temperature runs about 185 µP, which is 1.85 × 10⁻⁵ Pa·s since a micropoise is 10⁻⁷ Pa·s. Apply the plain poise factor to 185 and you get 18.5 Pa·s, somewhere near heavy honey. The obvious version announces itself; the subtle version drops only some of the decades.
Both forms are small decimals
Water is 0.01 P and 0.001 Pa·s. A moderately viscous oil might be 5 P and 0.5 Pa·s. Neither form looks obviously wrong sitting on a page, so a conversion that never happened tends to survive a read-through. The only reliable check is directional: the pascal-second figure is always the smaller of the two, by exactly one decimal place.
Legacy tables often omit the conditions
A viscosity in poise with no stated temperature — and for a gas, no stated pressure — cannot be set against a modern measurement however carefully it is converted. When the source is a review or a compilation rather than the original work, conditions are the first thing to have been dropped in transcription. Converting is the easy half; establishing what the number describes is the rest.