rasstre - Yes, there is a solution to this problem. I'm sure you can change inches to cm and keep the correct ratio of your thumbnail to similar image if you use this online converter https://www.inchestocm.com/ . I know that sometimes even such simple tasks as calculating the ratio in different metric systems can become a problem when you are too busy with your work and don't think about other things, so I hope that I could make it easier for you and help in your project.