Hi, I'm Shamim Hossain
Answer some questions and I will help you to figure out the right CSS unit for your project.
Assuming you are only using these units for web development, not for print media.
fr
The fr unit uses the leftover space. If you have three columns each with 1fr, they will adapt to whatever space is available, and generally all be the same size. It tends to be the best choice. % can also work, but can lead to overflow if you don't take into account gaps, whereas fr avoids that issue.