Wall art sizing - how to convert between inch and cm?
If you are seeing online store references that sell items manufactured for US sales primarily, the inch figures are more likely going to be accurate. The conversion results, for your example, in 35.56 cm, but for marketing purposes, rounding is acceptable. 

I have no experience in metric-following countries, but I would expect the reverse to be true. It is practical to expect a metric-sized frame to be 35 cm, but if it is going to list the imperial measurement, it would list it as 14 inches, rather 13.xx inches.

If measurements have to be precise for your purposes, ensure that the specifications are clearly listed, or request same from the vendor. I have purchased imperial-based items but required to know the accurate metric dimensions for a project. The vendor in both cases was able to provide more accurate numbers than the marketing copy listed.