Poise ↔ Stokes Converter
Convert dynamic viscosity (poise, centipoise, Pa·s, lb/ft·s) to kinematic viscosity (stokes, centistokes, m²/s, ft²/s) — and back — through fluid density with ν = μ/ρ. Includes real fluid presets. 100% client-side, no data leaves your browser.
Converter
Fluid presets (20 °C reference)
Quick unit conversion (no density needed)
Within the same viscosity family, conversion is a fixed factor — density is only needed when crossing between dynamic and kinematic.
Poise vs stokes: dynamic vs kinematic viscosity
Poise — dynamic viscosity (μ)
CGS unit of dynamic (absolute) viscosity: a fluid's internal resistance to shear flow. 1 P = 0.1 Pa·s; 1 cP = 1 mPa·s. Think: how "thick" the fluid feels when you stir it.
Stokes — kinematic viscosity (ν)
CGS unit of kinematic viscosity: dynamic viscosity divided by density (ν = μ/ρ). 1 St = 10⁻⁴ m²/s; 1 cSt = 10⁻⁶ m²/s. Think: how fast the fluid drains under its own weight — gravity matters, so density is in the picture.
Scope boundary — what this tool does not do
- No temperature modelling: viscosity is strongly temperature-dependent; presets are 20 °C references only.
- Newtonian fluids only: shear-thinning or shear-thickening fluids need rheometer data, not a unit converter.
- No Saybolt / Redwood efflux-time seconds conversion and no Reynolds-number calculation (those need velocity and length inputs).
- Density itself is an input here — if you need to convert density units first, use our density converter.
Frequently asked questions
What is the difference between poise and stokes?
Poise (P) measures dynamic viscosity — a fluid's internal resistance to flow — while stokes (St) measures kinematic viscosity, which is dynamic viscosity divided by density. Poise answers 'how thick is it'; stokes answers 'how fast does it flow under gravity'. In SI units these are pascal-second (Pa·s) and square metre per second (m²/s).
How do I convert poise to stokes?
You need the fluid's density. First convert poise to Pa·s (multiply by 0.1), divide by density in kg/m³ to get m²/s (ν = μ/ρ), then convert m²/s to stokes (multiply by 10,000). This converter does all three steps automatically when you enter a density.
What is the formula to convert dynamic viscosity to kinematic viscosity?
ν = μ / ρ, where ν is kinematic viscosity (m²/s), μ is dynamic viscosity (Pa·s), and ρ is density (kg/m³). Example: water at 20 °C has μ = 0.001002 Pa·s and ρ = 998 kg/m³, so ν = 0.001002 / 998 = 1.004 × 10⁻⁶ m²/s = 1.0040 cSt.
How many pascal-seconds are in one poise?
Exactly 0.1 Pa·s. The poise is the CGS unit of dynamic viscosity, so 1 P = 0.1 Pa·s and 1 centipoise (cP) = 0.001 Pa·s = 1 mPa·s.
How many m²/s are in one stokes?
Exactly 1 × 10⁻⁴ m²/s. The stokes is the CGS unit of kinematic viscosity, so 1 St = 1 cm²/s = 10⁻⁴ m²/s and 1 centistokes (cSt) = 1 mm²/s = 10⁻⁶ m²/s.
Can I convert centipoise directly to centistokes?
Only if you know the density. For water at 20 °C (density ≈ 998 kg/m³) the numbers are nearly identical: 1.002 cP ≈ 1.004 cSt. For oils or glycerin they differ enormously — glycerin's 1412 cP becomes 1120.6 cSt. Never convert without density except for water-like fluids.
Which density unit should I enter?
Any of kg/m³, g/cm³, or lb/ft³ — the converter normalises to kg/m³ internally. Water is 1000 kg/m³ = 1 g/cm³ ≈ 62.43 lb/ft³.
What is the kinematic viscosity of water at 20 °C?
1.0040 cSt (1.0040 × 10⁻⁶ m²/s). Water's dynamic viscosity at 20 °C is 1.002 cP and its density is 998 kg/m³, so ν = 0.001002 / 998.
What is the kinematic viscosity of glycerin?
About 1120.6 cSt at 20 °C. Glycerin's dynamic viscosity is 1.412 Pa·s (1412 cP) and its density is 1260 kg/m³, so ν = 1.412 / 1260 = 1.1206 × 10⁻³ m²/s.
What does lb/(ft·s) mean in viscosity?
It is the imperial unit of dynamic viscosity, equal to 1.4881639 Pa·s. It appears in US fluid-mechanics textbooks and older pipe-flow calculations.
How big is one ft²/s in kinematic viscosity?
0.09290304 m²/s, or 929.0304 St. It is the imperial counterpart of the stokes.
Why are motor-oil grades given in centistokes?
Kinematic viscosity in cSt is the industry standard (SAE J300, ASTM D445): an SAE 30 oil is roughly 90–110 cSt at 100 °C, measured by how long oil takes to drain through a calibrated capillary — a direct kinematic measurement.
Does temperature change the result?
Dramatically. Oil viscosity can halve with a 10–20 °C rise. The presets here are fixed at 20 °C reference values; enter your own measured viscosity and density if your fluid is at another temperature. This tool does not model temperature dependence.
Is this converter private? Does my data leave my browser?
Yes, it is fully private. Every calculation runs in JavaScript on your device; nothing is uploaded, stored, or tracked.
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