All multi-viscosity oils will have two sets of numbers. The top (larger) number shows the viscosity of the oil.
The most common oil viscosity measurement is called kinematic viscosity, which measures how fast oil will flow through a glass tube that is heated to 100 degrees Celsius (212F) when pulled through gravity. You can get the best motor oil via https://lambertoil.ca/our-products/other-products/
First, they are both 30 weight motor oils and there is no difference at all when either is in an engine at operating temperature. So both a 5W/30 and a 10W/30 have the same resistance to flow, the oil’s viscosity, when the engine is running and warmed up to operating temperature.
At cold temperatures though, the use of additives and or polymer technology allow the motor oil to flow more readily, i.e. a 5W/30 motor oil will flow more easily at low temperatures than a 10W/30 and a 0W/30 will flow better still at low temperatures making them more suited to winter use than the 10W/30
This is why the old practice of changing straight-grade oils to a heavier viscosity in the summer and a lighter viscosity in the winter is no longer necessary.
So if 0W/30, 5W/30 and 10W/30 are all 30 weight motor oils at operating temperature (kinematic viscosity of 9.3 to 12.5 centistokes at 100 C.) how is the lower winter rating number determined?
The winter or cold weather rating uses two measurements called Brookfield cranking viscosity and Brookfield pumping viscosity, both measured in units knows as centipoise.