About the Storage Capacity Calculator
Usable storage after RAID and formatting overhead, and how many files of a given size will fit.
Also known as: raid capacity calculator, usable disk space, how many photos fit, drive capacity.
How to use this calculator
- Enter drive size, number of drives, raid level, average file size.
- The result updates instantly as you type — press Calculate (or Enter) at any time.
- Review the breakdown shown under the main result.
- Use Copy result or Share to save the answer or send a link with your inputs.
Formula
usable = (drives − parity) × drive size, then decimal TB → binary TiB
Worked example
Using the values pre-filled in the calculator above:
- Drive size = 4 TB
- Number of drives = 4
- RAID level: RAID 5 (one parity drive)
- Average file size = 25 MB
the calculator returns:
- Usable capacity: 10.696 TiB
- As the manufacturer states it: 12 TB
- Raw total: 16 TB
- Lost to redundancy: 4 TB