Viscosity - Kinematic Converter
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| Unit | Equivalent Value |
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Kinematic Viscosity (also known as Momentum Diffusivity, Gravity Flow Resistance, or Dynamic-to-Density Ratio, symbolized by ν) measures a fluid’s inherent resistance to flow under the influence of gravitational force alone (ν = μ ÷ ρ, where μ is dynamic viscosity in Pa·s or cP and ρ is fluid mass density in kg/m3 or g/cm3). Across industrial hydraulic machinery oil selection (ISO VG grades), automotive engine motor oil viscosity rating (SAE J300 standard), marine heavy fuel oil (HFO) pre-heating control, turbine lubricant monitoring, aerodynamic boundary layer momentum diffusion, and capillary viscometry, kinematic viscosity is categorized across three major engineering unit families: International System of Units (SI metric fundamental: Square Meter per Second / m2/s, Square Millimeter per Second / mm2/s, Square Meter per Hour / m2/h), CGS Fluid Rheology standards (Stokes / St, Centistokes / cSt, Millistokes / mSt, Square Centimeter per Second / cm2/s), and Imperial US/UK Engineering metrics (Square Foot per Second / ft2/s, Square Foot per Hour / ft2/h, Square Inch per Second / in2/s).
Our free online Viscosity – Kinematic Converter provides instant, high-precision conversions across all SI metric, CGS centistokes, ISO VG hydraulic oil, and fluid mechanics momentum diffusivity units:
- Centistokes to mm2/s & m2/s [Exact 1:1 Identity]:
1 cSt = 1.0 mm2/s = 0.000001 m2/s = 0.01 Stokes (St) = 1.0 × 10-6 m2/s. - Stokes to Centistokes & m2/s [CGS Metric Standard]:
1 Stokes (St) = 100.0 cSt = 100.0 mm2/s = 0.0001 m2/s = 1.0 cm2/s. - Square Meter per Second to Centistokes [SI Base Unit]:
1 m2/s = 1,000,000.0 cSt = 10,000.0 Stokes (St) = 1,000,000.0 mm2/s. - Square Foot per Second to Centistokes & m2/s [US Imperial Standard]: Multiply ft2/s by
92,903.04(1 ft2/s = 0.09290304 m2/s = 92,903.04 cSt = 929.0304 St). - Square Inch per Second to Centistokes [US Pipe Standard]: Multiply in2/s by
645.16(1 in2/s = 645.16 cSt = 0.00064516 m2/s = 6.4516 St). - Square Foot per Hour to Centistokes [HVAC Duct Standard]: Multiply ft2/h by
25.8064(1 ft2/h = 25.8064 cSt = 0.0000258064 m2/s = 0.258064 St).
Master Kinematic Viscosity (Momentum Diffusivity) Conversion Table
The table below displays exact mathematical conversion relationships, SI m2/s multipliers, and centistokes (cSt / mm2/s) equivalents relative to 1 Centistokes (1 cSt = 1 mm2/s = 0.01 St):
| Kinematic Viscosity Unit Name | Symbol | Exact Value in m2/s | Centistokes (cSt) & mm2/s Equivalent | Domain & Technical Application Standard |
|---|---|---|---|---|
| 1 Centistokes | cSt, mm2/s |
0.000001 m2/s (10-6 m2/s) |
1.0 cSt (1.0 mm2/s) (0.01 Stokes / 0.0001 m2/h) |
Global ISO VG Lubricant & Petroleum Industry Standard |
| 1 Square Millimeter per Second | mm2/s |
0.000001 m2/s |
1.0 cSt (100% mathematically equal to 1.0 cSt) |
SI Derived Unit of Kinematic Viscosity |
| 1 Stokes | St, cm2/s |
0.0001 m2/s |
100.0 cSt (100.0 mm2/s / 0.360 m2/h) |
CGS Fundamental Unit (Named for Sir George Gabriel Stokes) |
| 1 Square Meter per Second | m2/s |
1.0 m2/s (Base SI Unit) |
1,000,000.0 cSt (10,000.0 St / 3,600.0 m2/h) |
SI Fundamental Momentum Diffusivity Metric |
| 1 Square Foot per Second | ft2/s |
0.09290304 m2/s |
92,903.04 cSt (929.0304 St / 334.451 m2/h) | US Imperial Hydraulic & Aerodynamic Momentum Diffusion |
| 1 Square Inch per Second | in2/s |
0.00064516 m2/s |
645.16 cSt (6.4516 St / 2.32258 m2/h) | US Imperial Valve & Orifice Flow Viscosity Rating |
| 1 Square Foot per Hour | ft2/h |
0.0000258064 m2/s |
25.8064 cSt (0.258064 St / 0.092903 m2/h) | Building HVAC Thermal & Moisture Momentum Transfer |
Step-by-Step ISO VG Hydraulic Oil & Motor Oil Viscosity Calculation Example
To convert an ISO VG 46 hydraulic machine oil with a kinematic viscosity of 46.0 Centistokes at 40°C (46.0 cSt or 46.0 mm2/s) into SI m2/s, CGS Stokes (St), and Imperial ft2/s:
Step 1 (SI m2/s Conversion): ν = 46.0 cSt × 0.000001 = 0.0000460 m2/s (4.60 × 10-5 m2/s)
Step 2 (CGS Stokes Conversion): ν = 46.0 cSt ÷ 100 = 0.460 Stokes (0.460 St)
Step 3 (Imperial ft2/s Conversion): ν = 46.0 cSt ÷ 92,903.04 = 0.00049514 ft2/s (4.951 × 10-4 ft2/s)
Thus, ISO VG 46 hydraulic oil has a kinematic viscosity of 4.60 × 10-5 m2/s, 0.460 Stokes, or 0.000495 ft2/s.
Real-World Kinematic Viscosity & Momentum Diffusivity Benchmarks
Below is a comparative reference chart showing kinematic viscosity values (ν) across air, water, motor oils, hydraulic fluids, and heavy fuel oils:
| Fluid Medium / Industrial Lubricant | Kinematic Viscosity in cSt (mm2/s) | SI & CGS Equivalent (m2/s / Stokes St) | Fluid Dynamics & Tribology Engineering Context |
|---|---|---|---|
| Pure Liquid Water (20°C / 68°F) | 1.0034 cSt (1.0034 mm2/s) | 1.0034 × 10-6 m2/s (0.010034 St) | Universal baseline reference for liquid gravity flow |
| Ambient Air (20°C, 1 atm – Momentum Diffusivity) | 15.16 cSt (15.16 mm2/s) | 1.516 × 10-5 m2/s (0.1516 St) | Air momentum diffusivity is 15x higher than water due to low air density! |
| ISO VG 32 Industrial Hydraulic Machinery Oil (40°C) | 32.0 cSt (32.0 mm2/s) | 3.20 × 10-5 m2/s (0.320 St) | Standard light industrial hydraulic pump oil viscosity |
| SAE 10W-30 Automotive Engine Motor Oil (40°C) | 68.0 – 75.0 cSt (68 – 75 mm2/s) | 6.8 – 7.5 × 10-5 m2/s (0.68 – 0.75 St) | Multi-grade passenger car engine oil operating kinematic viscosity |
| ISO VG 220 Industrial Heavy Gear Lubricant (40°C) | 220.0 cSt (220.0 mm2/s) | 0.000220 m2/s (2.20 Stokes St) | Heavy industrial gearbox & bearing lubrication rating |
| Marine Heavy Fuel Oil (HFO / Bunker C at 50°C) | 380.0 cSt (380.0 mm2/s) | 0.000380 m2/s (3.80 Stokes St) | Commercial ship engine heavy fuel oil atomization limit |
| Pure Liquid Glycerin (20°C / 68°F) | 1,180.0 cSt (1,180 mm2/s) | 0.001180 m2/s (11.80 Stokes St) | High-density liquid momentum diffusion benchmark |
History & Physics: 1851 George Stokes Drag Law vs ASTM D2161 Saybolt Seconds (SUS)
1851 Sir George Gabriel Stokes & The Stokes Unit (1 St = 1 cm2/s)
In 1851, Anglo-Irish mathematician and physicist Sir George Gabriel Stokes derived the hydrodynamic friction drag force acting on spherical objects moving through viscous fluids (Stokes’ Law: Fd = 6 · π · μ · r · v). Stokes introduced Kinematic Viscosity (ν = μ ÷ ρ) as momentum diffusivity. To honor his contributions, the CGS unit was named the Stokes (St), where 1 cSt = 1 mm2/s = 0.01 St.
ASTM D2161 Saybolt Universal Seconds (SUS) to Centistokes (cSt) Bridge
In early 20th-century petroleum refineries, kinematic viscosity was measured empirically by timing how many seconds 60 mL of oil took to flow through a calibrated orifice in a Saybolt viscometer, reported as Saybolt Universal Seconds (SUS). In 1933, ASTM D2161 standardized the conversion formula to fundamental centistokes: cSt ≈ 0.226 · SUS - (195 ÷ SUS) (for SUS > 100, cSt ≈ 0.220 · SUS).
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Frequently Asked Questions (FAQ)
Is 1 centistokes (cSt) identical to 1 mm2/s?
Yes, 1 centistokes (cSt) is 100% mathematically identical to 1 square millimeter per second (1 mm2/s). Both units represent exactly 0.000001 square meters per second (1.0 × 10-6 m2/s).
How do you convert centistokes (cSt) to Stokes (St)?
To convert Kinematic Viscosity from centistokes (cSt) to Stokes (St), divide by 100 (or multiply by 0.01). For example, ISO VG 46 oil (46 cSt) ÷ 100 = 0.46 Stokes (0.46 St).
How do you convert Saybolt Universal Seconds (SUS) to cSt?
For Saybolt viscometer times above 100 seconds, multiply SUS by approximately 0.220 to get cSt. For example, 150 SUS oil × 0.220 = 33.0 cSt (approx. ISO VG 32 oil).
Why does air have a HIGHER kinematic viscosity than water at room temperature?
Kinematic viscosity is dynamic viscosity divided by density (ν = μ ÷ ρ). Although water has higher dynamic viscosity (1.0 cP vs. air’s 0.018 cP), air’s mass density is so much lower (1.20 kg/m3 vs. water’s 998 kg/m3) that air’s kinematic viscosity (15.16 cSt) is 15 times larger than water’s (1.0 cSt).