Understanding kinematic viscosity
Kinematic viscosity is dynamic viscosity divided by density: the “goopiness” you feel after gravity and mass cancel in the bookkeeping. Turbine folks, bearing people, and oil labs often speak in centistokes while CFD teams want square meters per second. Convert here, then argue about Reynolds number with cleaner numbers.
How kinematic viscosity conversion works
SI keeps ν in m²/s. One stokes equals 10⁻⁴ m²/s in SI, which makes one centistokes land at 10⁻⁶ m²/s. Square feet per second merely swaps area units on top of that story using the international foot definition.
Result = Value × (source as m²/s per unit) ÷ (target as m²/s per unit)
Hour-based rows slow the clock without touching length, so ft²/h is not the same shortcut as ft²/s with a stray 3600 borrowed from somewhere else.
Friendly unit names on the chart
The stokes family stretches from atto- to exa- for archival reasons. These are the ones people still say out loud.
Square meter per second [m²/s]
Factor: 1 (base)
The straight SI kinematic viscosity. Rarely handy for intuition, excellent for software.
Square meter per hour [m²/h]
Factor: m² spread over an hour length in seconds
Some HVAC spreadsheet macros hide hourly ν this way. Confirm whether they meant dynamic viscosity before you assume kinematic.
Stokes [St]
Factor: 1e-4 m²/s per stokes
CGS comfort food. One hundred centistokes make one stokes in case someone mixes wording mid sentence.
Centistokes [cSt]
Factor: 1e-6 m²/s per cSt
Lubricant grades and jet fuel specs still float here. Roughly matches millimeters squared per second with SI prefixes.
Square centimeter per second [cm²/s]
Factor: 1e-4 m²/s (same numeric as stokes)
Handy when diagrams show centimeter scale channels. Not the same thing as dynamic poise unless you chase the correct definition path.
Square foot per second [ft²/s]
Factor: international square foot area
Imperial pipe books sometimes park ν this way next to duct areas also in square feet.
Common kinematic viscosity conversions at a glance
Patterns that behave when you leave the textbook behind.
| From | To | Pattern | Example |
|---|---|---|---|
| St | m²/s | × 1e-4 | 1 St = 1e-4 m²/s |
| cSt | m²/s | × 1e-6 | 1 cSt = 1e-6 m²/s |
| mm²/s | cSt | 1:1 numeric | Handy mnemonic |
| m²/h | m²/s | ÷ 3600 | 3600 m²/h = 1 m²/s |
| ft²/s | m²/s | × 0.09290304 | Exact ft² factor |
| in²/s | m²/s | × 0.00064516 | Small channels |
Remember ν is not the whole fluid story
Density ties ν back to μ. If someone hands you kinematic viscosity without saying which fluid or temperature produced it, treat the number like a postcard without a postmark: pretty, but thin on context.
Mixtures with sliding composition may need curves, not constants. Conversion only preserves the numeric relationship between labels you already trust.
Kinematic viscosity FAQ
Is cSt the same as mm²/s?
Numerically yes: one centistokes lines up with one square millimeter per second in SI length units.
Why are there so many stokes prefixes?
Reference tables sometimes go wide to cover every stray datasheet. Pick the prefix that matches your source and ignore the rest until you actually need them.
Does hour-based ν differ from hour-based flow?
Different quantity, same time trick: hours always bring 3600 seconds with them once you unfold the rate properly.
Can I rebuild μ from ν?
Multiply ν by ρ at the same temperature and pressure path you trust. Garbage ρ gives garbage μ.