Take a look at this post and the excel file linked further in the thread. This can give you an idea of how quickly your system might be storing data. If it works for your application, consider enabling pruning for old historical data.
If you can clear up enough disk space to run for e.g. a week, you can also do real world benchmarking. Extrapolate from a week to whatever pruning rate you need, and you'll get a rough idea of your bare minimum storage requirements. Give yourself a healthy safety margin to account for variance and system expansion over time.