Eng Unit Converter

Dynamic (absolute) viscosity measures a fluid's internal resistance to shear flow, describing how much force is needed to move one layer of fluid past another. The SI unit is pascal-second (Pa·s), but centipoise (cP) is the practical standard in industry. Key conversions: 1 Pa·s = 1,000 cP = 10 poise, 1 cP = 0.001 Pa·s = 1 mPa·s. Reference values: water ≈ 1 cP at 20°C, honey ≈ 2,000–10,000 cP, motor oil SAE 30 ≈ 150–200 cP at 40°C, air ≈ 0.018 cP at 20°C. Viscosity is essential in pipe flow calculations (pressure drop via Darcy-Weisbach), pump selection, lubrication engineering, polymer processing, food manufacturing, and pharmaceutical formulation. Critical pitfalls: confusing dynamic viscosity (cP, Pa·s) with kinematic viscosity (cSt, m²/s) — they are related by density (ν = μ/ρ). For water cP ≈ cSt, but for oil at 0.9 g/cm³ the values differ by 10%. Also note that 1 P = 0.1 Pa·s, not 0.01, which is a frequent conversion error.