How to use the Storage Capacity Calculator
Enter the advertised storage size, then subtract a realistic system reserve for the operating system, built-in apps, cache, and updates. The calculator estimates usable storage and converts that space into photos, video time, apps, music tracks, and documents.
This is useful when choosing between 64GB, 128GB, 256GB, 512GB, and 1TB phone or tablet models. If you record video often, focus on the video bitrate setting because video is usually the fastest way to fill storage.
If you are comparing phone displays, use the Phone Screen Size Comparison Calculator. If you are planning charging and travel use, check the Battery Charging Time Calculator.
Storage capacity formula
usable storage = advertised storage - system reservephotos = usable MB / average photo MBvideo minutes = usable MB x 8 / video bitrate Mbps / 60apps = usable MB / average app MBDevice storage is often sold as decimal gigabytes, so this calculator uses 1 GB = 1000 MB for planning. Real devices may show a slightly different value depending on operating system reporting and reserved partitions.
Assumptions and methodology
The calculator estimates usable storage after system reserve, then divides that space by file-size assumptions. It does not scan your device or predict app cache growth, but it gives a transparent way to compare storage options before buying.
- Advertised storage is treated as decimal GB or TB for simple product comparison.
- System reserve should include the operating system, preinstalled apps, updates, cache, and a little free-space buffer.
- Photo estimates depend on average photo size. RAW, ProRAW, HDR, and high-megapixel modes can be much larger.
- Video estimates use bitrate because resolution labels alone do not define file size.
Example calculations
128GB phone storage example
A 128GB phone with a 20GB system reserve leaves about 108 GB usable. At 4 MB per photo, that is about 27,000 photos if the space is used only for photos.
With 60 Mbps video, the same usable space holds about 4 hr of video. At 250 MB per app, it could fit about 432 apps, although real apps often grow with downloads and cache.
Storage capacity chart
These examples use 4 MB photos, 60 Mbps video, and 250 MB average app size. System reserve increases slightly for larger storage options.
| Advertised | Usable | Photos | 4K video | Apps |
|---|---|---|---|---|
| 64 GB | 49 GB | 12,250 | 1 hr 49 min | 196 |
| 128 GB | 108 GB | 27,000 | 4 hr | 432 |
| 256 GB | 231 GB | 57,750 | 8 hr 33 min | 924 |
| 512 GB | 477 GB | 119,250 | 17 hr 40 min | 1,908 |
| 1 TB | 950 GB | 237,500 | 35 hr 11 min | 3,800 |
Popular phone storage questions
These focused answers cover common buying questions that need a direct estimate before using the full calculator.
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FAQ
How do I calculate storage capacity?
Start with the advertised storage, subtract system and reserved storage, then divide the usable storage by the average file size. For video, use bitrate: higher bitrate video uses more storage per minute.
How many photos can 128GB hold?
With the default assumptions on this Storage Capacity Calculator, 128GB with a 20GB system reserve leaves about 108 GB usable. At 4 MB per photo, that fits about 27,000 photos if the storage were used only for photos.
How much 4K video can 128GB hold?
Using the default 60 Mbps 4K video estimate and 108 GB usable storage, 128GB can hold about 4 hr of video if used only for video.
Is 128GB enough for a phone?
128GB is usually enough for light to moderate use, especially with cloud photos and streaming. It can feel tight if you record a lot of 4K video, keep many offline downloads, or install large games.
Should I choose 128GB or 256GB?
Using the reference assumptions, 256GB leaves about 231 GB usable after a 25GB reserve, more than double the usable space of a typical 128GB model. Choose 256GB if you keep videos, games, or offline media on the device.
Why is usable storage less than advertised storage?
Phones and tablets reserve space for the operating system, built-in apps, updates, cache, logs, and sometimes recovery partitions. The number shown in settings can also use a different GB/GiB display convention.
Why do photo and video estimates vary so much?
File size depends on resolution, compression, format, frame rate, HDR, bitrate, editing, and app settings. Treat the result as a planning estimate and adjust the average photo size or video bitrate if you know your device settings.