How to use
1. Pick a category. 2. Choose the units on both sides — the ⇄ button swaps them instantly. 3. Type a value: the result and the exact 1 from-unit = … to-unit factor update live. Every category also carries a quick-ladder table of the most-used pairs, and the right column keeps the three daily combos ready. All factors are stored to full precision and shown to 7 significant digits; values marked empirical are engineering approximations, not definitions.
Viscosity: why SSU ↔ cSt is not a simple factor
The Saybolt seconds universal scale is a timing scale, not a physical unit: efflux time grows faster than linearly with kinematic viscosity because of capillary-tube entrance effects. The straight 4.635 multiplier is only trustworthy from about 70 cSt upward. Below that, use the pair tables — e.g. \(1.0\ \text{cSt} = 31\ \text{SSU}\), \(20.6\ \text{cSt} = 100\ \text{SSU}\), \(53\ \text{cSt} = 250\ \text{SSU}\) — where the effective multiplier falls from ≈31 to ≈4.7. The converter marks SSU (and Engler) values as empirical for exactly this reason.
Converting between dynamic and kinematic families needs density, not another factor:
$$\nu\,(\text{cSt}) \;=\; \frac{\mu\,(\text{cP})}{SG} \qquad\text{(where density in g/cm}^3 \text{ equals } SG)$$When a category mixes the two families (kinematic ↔ dynamic), the converter solves it with your SG in the combos panel — or flags the row instead of pretending a silent factor exists.