Here are is the definition under ASTM D5293 for cold cranking.
Cold Crank Viscosity
ASTM D5293- Test Method for Apparent Viscosity of Engine Oils Between -5 and -35 C Using the Cold Crank Simulator
This test method covers the laboratory determination of apparent viscosity of engine oils at temperatures between –5 and -35C and at high shear rates. The results are related to engine cranking characteristics of engine oil. A measured amount of sample is subjected to an extreme low temperature for 3 minutes. The rotor spins for 1 minute in the sample and the speed of the rotor is measured by keeping ohms resistance at zero. The speed-reading is used to determine the viscosity on a calibration curve.
The cold cranking simulator (CCS), ASTM D5293, correlates with engine cranking speed at low temperatures.
Cold cranking viscosity simulates the viscosity of an oil in crankshaft bearings during cold temperature start up.
Cold cranking viscosity limits, determined by the CCS, are defined in the SAE J300 Standard, as shown below:
Cold Crank Viscosity
Low temperature viscosity (mPa s) Max (CCS) Temps are degrees C.
0W 6200 @ -35
5W 6600 @ -30
10W 7000 @ -25
15W 7000 @ -20
20W 9500 @ -15
25W 13000 @ -10