Storage Needed Calculator
Sizing a drive, backup target or cloud bucket comes down to a simple product:
total = number of files × average file size × (1 + headroom)
Enter how many files you have, their average size, and a little headroom for growth and filesystem overhead. So 5000 photos at 4 MB each with 20% headroom needs about 24 GB.
Results are shown in MB, GB and TB using decimal units (1 GB = 1000 MB), the same way drives are advertised — so the number maps straight onto what you would buy. Everything is calculated locally in your browser, with nothing sent anywhere.