Computers & Laptops

Storage Capacity Calculator

How much storage a set of files needs, from how many there are and how big they average.

4 inputs Free, no sign-up

Your figures

Spare room above the files themselves. A drive filled to the last byte slows down, and an SSD needs free blocks for wear levelling.

Try an example

Result

Your result

Enter your figures and the result appears here.

Estimates only. Rates, fees and specifications change. Confirm against the official source before you rely on a figure — see our disclaimer.

About this calculator

A count and an average give a total. Twenty thousand photographs at four megabytes each is eighty gigabytes, and knowing that before buying a drive is the whole point.

The result is shown in both conventions — decimal GB as drives are sold, and binary GiB as your operating system will report — because the two differ by about 7% at that scale.

How to use this calculator

  1. Enter how many files you have.
  2. Enter the average size of one. Your file manager shows a folder's total and its count; the average is one divided by the other.
  3. Set a margin if you want room to spare.

The formula

Total = Number of files x Average size
With margin = Total x (1 + margin / 100)
SymbolMeaningUnit
Files How many you have
Average Average size of one MB
Margin Spare room you want %

Worked example

5,000 files averaging 4.2 MB, with a 20% margin:

5,000 x 4.2 = 21,000 MB = 21 GB
21 x 1.20    = 25.2 GB (which is 23.47 GiB)

Notes and limits

  • An average is an average. A folder with a handful of very large files in it will not match this closely.
  • Small files waste space on a filesystem: each one occupies at least a whole allocation unit, so a hundred thousand tiny files take noticeably more room than their total suggests.
  • A drive should not be filled to the last byte. Filesystems slow down when nearly full, and an SSD's wear levelling needs free blocks to work with.
  • To convert any figure between units, use the storage unit converter.

What this calculation assumes

  • The average is treated as exact, which it never is.
  • Filesystem overhead from small files is not included.
  • The result states which convention it counted in and shows the other alongside.

Frequently asked questions

How much storage do I need for 5,000 photos?

Multiply by the average size. At 4.2 MB each that is 21 GB, or about 25 GB with a fifth left spare. Phone photos and raw camera files differ by a factor of ten, so use your own average.

Why does the answer show two different figures?

Because storage is sold in decimal gigabytes of 1,000,000,000 bytes and reported by most operating systems in binary ones of 1,073,741,824. Both describe the same data; the labels differ.

How do I find my average file size?

Select a folder and look at the properties: it gives the total size and the number of files. Divide one by the other.

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