Figuring out how much storage you actually need — for a photo library, a game collection, a video project, or a backup set — usually starts with rough guessing and ends with a drive that’s either way oversized or unexpectedly full. This calculator adds up file sizes and counts to give you a clearer total, and checks it against the drive space you have available.
| Average file size | 500GB | 1TB | 2TB |
|---|---|---|---|
| 5MB | 100,000 | 200,000 | 400,000 |
| 50MB | 10,000 | 20,000 | 40,000 |
| 500MB | 1,000 | 2,000 | 4,000 |
| 50GB | 10 | 20 | 40 |
Decimal units (1GB = 1,000MB), as drive makers count. Windows shows a 1TB drive as about 931GB because it counts in 1,024s.
How this is calculated: the formula on our Methodology page.
Quick answer
This tool adds up the sizes and quantities of files or media you describe into a total storage requirement, then checks that total against a drive’s usable capacity — accounting for the fact that a drive’s advertised decimal capacity (1TB equals 1,000,000,000,000 bytes) reads as a smaller number once an operating system displays it using binary-based units.
What Fits on 512GB, 1TB, 2TB and 4TB?
A 1TB drive holds about 225,000 phone photos, 88 hours of 4K video or 9 large games, keeping 10% of the drive free. Each line below is one kind of file on an otherwise empty drive; for a mix, enter your own sizes in the calculator above.
| File type | 512GB | 1TB | 2TB | 4TB |
|---|---|---|---|---|
| Photos (4MB each, a typical 12MP phone JPEG) | 115,200 | 225,000 | 450,000 | 900,000 |
| 1080p video, 30 fps (about 3.6GB an hour) | 128 | 250 | 500 | 1,000 |
| 4K video, 30 fps (about 10.2GB an hour) | 45 | 88 | 176 | 352 |
| Large games (100GB each) | 4 | 9 | 18 | 36 |
Decimal units, as drive makers count (1TB = 1,000GB). Video sizes are Apple’s per-minute figures for iPhone recording in HEVC; other cameras and codecs differ. Game sizes vary widely: many esports titles need well under 100GB, some big releases more. A system drive also holds Windows and its updates.
What the Result Means
The calculator totals the storage required for the files or file types you describe, then compares that total against the available capacity you enter for a target drive. The output tells you the total space needed, and whether it fits with room to spare, fits exactly, or exceeds what’s available — and by how much in either direction.
This is useful before buying a new drive (so you don’t overspend on capacity you’ll never use, or undersize one you’ll outgrow in months), and before starting a large copy or archive job where you want to confirm the destination has enough room before you start rather than finding out halfway through a multi-hour transfer.
How This Calculator Works
The core calculation is straightforward addition and unit conversion, but a few details make the estimate meaningful:
- Enter the size and quantity for each category of file (e.g. average photo size × number of photos, or total size of an existing folder).
- The calculator sums these into a total, normalizing everything to a common unit (typically GB).
- It then compares that total against your drive’s usable capacity, accounting for the fact that a drive’s listed capacity and its actual usable space in an OS aren’t quite identical.
Worked example: a photographer estimating a backup drive for a growing photo library:
- 40,000 RAW photos at an average of 25MB each = 1,000,000MB = 1,000GB (1TB)
- Plus roughly 200GB of edited exports and video clips
- Total needed: ~1,200GB (1.2TB)
- Against a 2TB drive showing ~1,863GB usable in the OS, that leaves roughly 660GB of headroom for future growth
That headroom figure is often the most practical output — it tells you not just whether something fits today, but how much runway you have before you’ll need more storage.
Important Limitations
- Advertised capacity isn’t usable capacity. Drive manufacturers label capacity using decimal units (1TB = 1,000,000,000,000 bytes), while operating systems typically report space using binary units, so a “2TB” drive usually shows closer to 1,863GB in Windows or macOS. This is normal, not a defect.
- File system overhead reduces usable space further. Formatting, the file system’s own metadata, and a reserved margin on some systems all take a small additional bite out of raw capacity.
- Average file sizes are estimates, not guarantees. Real photo, video, or document libraries have size variance — a batch of long 4K clips will use dramatically more space than the same count of short clips, so treat averages as a planning tool, not an exact prediction.
- Compression and deduplication aren’t accounted for. Some backup and archive tools compress or deduplicate data, which can make actual space used lower than a straight sum of original file sizes.
Frequently Asked Questions
Why does my new drive show less space than advertised?
Manufacturers use decimal units (1,000-based) for capacity labeling, while your operating system reports space in binary units (1,024-based). A 1TB drive showing roughly 931GB in Windows is expected behavior, not a shortage.
How much space should I leave free on a drive?
As a general guideline, leaving some free space (often cited as 10-20% on SSDs) helps maintain performance and gives room for temporary files, updates, and normal growth, though this matters less on traditional hard drives.
Does this calculator account for file compression?
No — it works from the raw sizes you enter. If your files will be compressed as part of a backup or archive process, actual space used may end up lower than the calculated total.
Can I use this to plan storage for a video project?
Yes. Enter your expected footage size per hour or per clip and multiply by your shoot length, then add margin for exports, project files, and backups — video projects tend to need more headroom than static file libraries.