Kinematic Viscosity & ISO Grade Converter

Tribology, Lubrication Engineering & Kinematic Viscosity Metrology

Kinematic Viscosity is the ratio of dynamic viscosity to fluid density, measuring resistance to flow under gravity:

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• Universal Kinematic Viscosity Conversion Formulas (ASTM D445 & ISO 3104)**:

1 cSt (Centistokes) 1 mm^2/s = 10^-6 m^2/s = 0.01 Stokes (St)

ν_ft^2/s = ν_cSt92,903.04 = ν_m^2/s × 10.7639

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• ASTM D2161 Saybolt Universal Seconds (SUS) Conversion**:

SUS ≈ 4.6324 × ν_cSt (for ν > 100 cSt)

SUS ≈ 4.6324 × ν_cSt + (195) / (ν_cSt) (for ν 100 cSt)

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• Interconversion with Dynamic Absolute Viscosity**:

μ (cP) = ν (cSt) × Specific Gravity = ν × ρ × 1,000

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• Standard Lubricant & Fluid Kinematic Viscosity Benchmarks**:

• Liquid Water (20°C): 1.004 cSt 31.0 SUS μ = 1.004 cP

• ISO VG 46 Hydraulic Oil: 46.0 cSt @ 40^ 215.1 SUS μ = 40.25 cP

• SAE 30 Motor Oil (40°C): 100.0 cSt 465.2 SUS μ = 88.00 cP

• ISO VG 220 Gear Oil: 220.0 cSt 1,020.8 SUS μ = 195.8 cP

How to Use This Calculator

Enter your Kinematic Viscosity Magnitude (ν) (e.g. 46.0 in ν), From Kinematic Viscosity Unit — choose from Centistokes (cSt = mm²/s - ISO 3448 Standard), Square Meters per Second (m²/s - SI Base Unit), Stokes (St = 100 cSt - CGS Unit), To Kinematic Viscosity Unit — choose from Saybolt Universal Seconds (SUS), Square Meters per Second (m²/s), Centistokes (cSt = mm²/s), Fluid Density (ρ in kg/m³ for Dynamic Viscosity µ) (e.g. 875 in kg/m³), and Lubrication & Industrial Fluid Benchmark — choose from Custom Kinematic Viscosity, ISO VG 46 Hydraulic Oil (46.0 cSt @ 40°C, ρ=875) → 215.1 SUS | 4.60 × 10⁻⁵ m²/s | µ = 40.25 cP, Liquid Water @ 20°C (1.004 cSt, ρ=1000) → 31.0 SUS | 1.004 × 10⁻⁶ m²/s | µ = 1.004 cP. Verify your units match the formula standard (SI vs imperial) before entering values.

The Formula

Dynamic Viscosity: mu = nu rho (in Pas -> cP)

Worked Example

An industrial plant maintenance technician replacing a legacy machine specifying 215 SUS lubricant determines that ISO VG 46 hydraulic oil (46.0 cSt) is the exact modern metric equivalent.

Understanding Your Result

Kinematic reference values: Speed of light 3×10⁸ m/s (c), speed of sound in air at 20°C 343 m/s, speed of sound in water 1,480 m/s, Earth's orbital speed 29.8 km/s. Acceleration due to gravity (g) = 9.81 m/s² at sea level (varies 9.78 at equator to 9.83 at poles). Relativistic effects become measurable above ~10% of the speed of light — classical kinematic formulas apply for everyday speeds. Unit conversions: 1 m/s = 3.6 km/h = 2.237 mph.