Is there a formula for converting a battery amp hour rating, which is used in much of Europe and Asia, to an Cold Cranking Amps (CCA) rating?
While you'd want to believe there's a relationship between CCA (or even CA) and AH, there really isn't a simple one. The reason you cannot just convert it over, even with a rule of thumb, is because the two different figures are usually used to show two different things.
The Cold Cranking Amps, or CCA, of a battery lets the owner know how much of a surge capacity a battery might have. IOW: How much power can a battery provide over a short period of time.
Amp Hours, or AH, of a battery lets the owner know how long the battery should be able to provide power at a certain rate. This is continued power over the long haul.
In general, you can say as you increase the CCA, the AH also increases.
A decent article on this very subject can be read here.
As Paulster2 suggested, CCA (cold cranking amps) and Amp-hours are not related. Trying to convert one into the other is like trying to convert miles per hour (MPH) into miles per gallon. While miles per hour do affect miles per gallon, it's not really a conversion you can make. They both reflect different performance characteristics of the vehicle. The same holds for CCA and Amp-hours: CCA is how much current the battery can supply in a short amount of time (usually 30 seconds), Amp-hours is how long the battery can output a certain current.
There is a rule of thumb doing the rounds AH * 7.25 = CCA, but this is not guaranteed as not all batteries are created equal....
And just to note, we here in Europe also use CCA as well - having just replaced my battery and definitely needing cold cranking amps in Switzerland...
So here's a listing for a battery, note the CCA shown (also note the AH*7.25 does not work...)... and here is the link to the website : https://www.tayna.co.uk/Varta-Car-Batteries-S218-1.html
I'm adding an answer here which addresses the underlying question of what to do if CA or CCA aren't listed, but something else is.
Basically, I've run across conversion tables between a variety of battery capacity measurement standards used in various parts of the world ( SAE = CCA ):
Another note of interest is that a battery tester and charger company named CTEK publishes a similar conversion table, and at the bottom it lists a rule of thumb to use if all you have available is the Amp Hour rating:
When testing a “leisure” battery without a CCA rating:
1) Multiply the battery’s Ah rating x 3 to find the approximate DIN rating.
2) Find the sum in the DIN column and look along the row to find the EN rating.
3) Input this figure into the analyzer and proceed with the testing.