1 Answer

a piston engine, there are two different ways of describing the stroke ratio of its cylinders, and these are often mixed together causing confusion. These are: bore/stroke ratio, and stroke/bore ratio.
[edit]Bore/stroke ratio
Bore/stroke is the most commonly used term, which is mainly used in North America, Europe, United Kingdom, Asia, Australia, and some other countries.
The diameter of the cylinder bore is divided by the length of the piston stroke to give the ratio.
[edit]Stroke/bore ratio
Stroke/bore ratio is generally more rare than bore/stroke ratio, but is used in some countries, like in Finland for example.
The length of the piston stroke is divided by the diameter of the cylinder bore to give the ratio.
Stroke/bore ratio is similar to the bore/stroke ratio with the following exception:
When stroke/bore value is over 1:1 the engine is long-stroke or undersquare and when the stroke/bore value is under 1:1 the engine is short-stroke or oversquare. The square engine has a value of 1:1 in both cases.
For example an engine with 110 millimetres (4.33 in) stroke and 80 millimetres (3.15 in) bore, stroke/bore value 1.375, is an undersquare or long-stroke engine. An engine that has 70 millimetres (2.76 in) stroke and 100 millimetres (3.94 in) bore, stroke/bore value 0.7, is oversquare or short-stroke.
[ (Source:  Wikipedia)   I hope this helps?}