Definition
A unit of kinematic viscosity equal to one one-hundredth of a stokes, used to express how easily a fluid flows under gravity at a specified temperature. One centistoke equals one square millimeter per second (1 mm²/s). It is the standard unit used in aviation to specify the viscosity of lubricating oils, hydraulic fluids, and fuels.
Plain English
A measurement of how thick or thin a fluid is — specifically, how easily it flows on its own. A low number means the fluid is runny like water; a higher number means it is thicker like cold oil.
Context Anchor
Seen in engine oil, fuel, and hydraulic fluid specifications in powerplant and maintenance data.
Derivation
Named after Sir George Stokes, a 19th-century British physicist who studied fluid motion. 'Centi-' is Latin for one-hundredth, so a centistoke is one-hundredth of a stokes. Knowing this anchors the unit to fluid-flow science rather than to anything about distance or weight.
Why Pilots Care
Using a fluid with the wrong viscosity can cause poor lubrication, hard cold-weather starts, sluggish hydraulic response, or component wear. Maintenance personnel match the fluid's centistoke rating at a given temperature to what the engine or system manufacturer requires.
Analogy
Think of water and cold syrup. Water has a low centistokes value because it flows easily; cold syrup has a higher value because it flows slowly.
Grounding Statement
Water at room temperature is about 1 centistoke; engine oil might be 100 centistokes when warm and several hundred when cold — the same oil, just thicker as it cools.
Intuition Check
Centistokes do not measure how much fluid there is. They measure how easily the fluid flows.
Example Sentence 1
The technician confirmed the hydraulic fluid met the 15 centistokes minimum specified at operating temperature.
Example Sentence 2
Fuel meeting the required centistokes specification flows correctly through the engine filters and injectors.