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Convert between all viscosity units including dynamic and kinematic viscosity
Note: Dynamic viscosity (Pa·s, cP, P) and kinematic viscosity (m²/s, cSt, St) cannot be directly converted without knowing the fluid's density. This converter shows conversions within each type.
Measures a fluid's internal resistance to flow. It represents the force required to move one layer of fluid past another.
Units: Pa·s, mPa·s, cP, P
Symbol: μ (mu) or η (eta)
Also called: Absolute viscosity
Measures how fast momentum diffuses through a fluid. It accounts for the fluid's density in addition to its resistance to flow.
Units: m²/s, cSt, St
Symbol: ν (nu)
Relationship: ν = μ / ρ
To convert between these types, you need the fluid's density (ρ):
Kinematic Viscosity (ν) = Dynamic Viscosity (μ) / Density (ρ)
Example: Water at 20°C
• Dynamic viscosity: 1 cP = 0.001 Pa·s
• Density: 1000 kg/m³ = 1 g/cm³
• Kinematic viscosity: 0.001 Pa·s / 1000 kg/m³ = 1 × 10⁻⁶ m²/s = 1 cSt
Pascal-seconds (Pa·s)
1 Pa·s = 1,000 mPa·s = 1,000 cP = 10 P
Centipoise (cP)
1 cP = 0.001 Pa·s = 1 mPa·s = 0.01 P
Poise (P)
1 P = 0.1 Pa·s = 100 cP
Square Meters per Second (m²/s)
1 m²/s = 1,000,000 cSt = 10,000 St
Centistokes (cSt)
1 cSt = 10⁻⁶ m²/s = 1 mm²/s = 0.01 St
Stokes (St)
1 St = 10⁻⁴ m²/s = 100 cSt
| Fluid (at 20°C) | Dynamic (cP) | Dynamic (Pa·s) | Kinematic (cSt) |
|---|---|---|---|
| Air | 0.018 | 0.000018 | 15 |
| Water | 1.0 | 0.001 | 1.0 |
| Milk | 3 | 0.003 | ~3 |
| Blood (37°C) | 3-4 | 0.003-0.004 | ~3-4 |
| Ethanol | 1.2 | 0.0012 | 1.5 |
| Mercury | 1.5 | 0.0015 | 0.11 |
| Vegetable Oil | 60-80 | 0.06-0.08 | 70-90 |
| SAE 10W Motor Oil | 65-90 | 0.065-0.09 | 75-100 |
| SAE 30 Motor Oil | 200-300 | 0.2-0.3 | 230-350 |
| SAE 50 Motor Oil | 400-600 | 0.4-0.6 | 460-700 |
| Castor Oil | 600-1000 | 0.6-1.0 | 650-1100 |
| Glycerin | 1,500 | 1.5 | 1,200 |
| Honey | 2,000-10,000 | 2-10 | 1,400-7,000 |
| Corn Syrup | 5,000-10,000 | 5-10 | ~4,000-8,000 |
| Peanut Butter | 150,000-250,000 | 150-250 | — |
Viscosity is highly temperature-dependent. For most liquids, viscosity decreases exponentially as temperature increases. This relationship is critical for engineering applications.
0°C: 1.79 cP
20°C: 1.00 cP
40°C: 0.65 cP
60°C: 0.47 cP
80°C: 0.35 cP
100°C: 0.28 cP
0°C: ~1,000 cP
20°C: ~250 cP
40°C: ~110 cP
60°C: ~50 cP
80°C: ~30 cP
100°C: ~18 cP
The Viscosity Index quantifies how much a fluid's viscosity changes with temperature. Higher VI means more stable viscosity across temperatures. Typical values: mineral oils (90-110), synthetic oils (120-160), water (very low, ~300 VI scale reversed).
The Society of Automotive Engineers (SAE) classifies motor oils by their viscosity at different temperatures. Multi-grade oils like "10W-30" perform across wide temperature ranges.
Example: 10W-30
| SAE Grade | Viscosity at 100°C (cSt) | Typical Use |
|---|---|---|
| 0W-20 | 5.6-9.3 | Fuel-efficient, cold climates |
| 5W-20 | 5.6-9.3 | Modern engines, cold starts |
| 5W-30 | 9.3-12.5 | Most common, all seasons |
| 10W-30 | 9.3-12.5 | Moderate climates |
| 10W-40 | 12.5-16.3 | High-mileage engines |
| 15W-40 | 12.5-16.3 | Diesel engines, hot climates |
| 20W-50 | 16.3-21.9 | Racing, very hot climates |
Characterizing crude oil, fuels, and lubricants. Pipeline design and pump selection depend critically on viscosity measurements.
Quality control for products like sauces, syrups, and dairy. Viscosity affects texture, flow, and consumer perception.
Formulating liquid medications, creams, and suspensions. Critical for dosage accuracy and application properties.
Controlling application properties, flow, and leveling. Viscosity determines spray patterns and finish quality.
Injection molding and extrusion of plastics. Melt viscosity determines processing conditions and final product properties.
Selecting hydraulic fluids for optimal power transmission, efficiency, and equipment protection across operating temperatures.
Dynamic viscosity (Pa·s, cP) measures internal friction without considering density. Kinematic viscosity (m²/s, cSt) is dynamic viscosity divided by density, representing how quickly momentum diffuses through the fluid. For water with density 1 g/cm³, they're numerically equal in CGS units (1 cP = 1 cSt).
Centipoise (cP) is dynamic viscosity while centistokes (cSt) is kinematic viscosity. You need the fluid's density to convert: cSt = cP / density (g/cm³). For water at 20°C with density 1 g/cm³, 1 cP equals 1 cSt, but this doesn't hold for other fluids.
Use dynamic viscosity (cP, Pa·s) when dealing with forces and stresses, like pump power calculations. Use kinematic viscosity (cSt, m²/s) for flow-related applications like pipe flow, Reynolds number, and ISO lubricant grades. Many industries prefer specific units based on tradition and convenience.
Newtonian fluids (water, oil) have constant viscosity regardless of shear rate. Non-Newtonian fluids change viscosity with applied stress. Examples: shear-thinning (paint, ketchup get thinner when stirred), shear-thickening (cornstarch solution thickens under stress), and viscoelastic (polymers show both viscous and elastic behavior).
Accuracy requirements vary: ±0.5% for critical applications like ISO reference fluids, ±1-2% for quality control, ±5-10% for process monitoring. Temperature control is crucial—viscosity can change 2-10% per °C. Always specify the temperature when reporting viscosity.
Rotational viscometers (dynamic viscosity via torque), capillary viscometers (kinematic viscosity via flow time), falling ball viscometers (Stokes' law), and vibrational viscometers (resonant frequency). Choice depends on viscosity range, sample volume, and whether you need dynamic or kinematic measurements.
Proper viscosity ensures adequate lubrication while minimizing friction. Too thick: hard cold starting, increased fuel consumption. Too thin: inadequate protection at high temperatures, increased wear. Multi-grade oils balance cold-start performance with high-temperature protection, which is why most modern vehicles use them.