Storage Size Calculator

Total a list of sizes and convert bytes to GB, GiB or bits, with the 1000-versus-1024 question spelled out beside the switch.

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What this tool does

Storage Size Calculator works two ways. Type a list of sizes, one per line, and it adds them together, giving each entry its byte count, its size in a readable unit and its share of the total; leave the box empty and it converts the single Value and Unit chosen beside it instead. A line may carry a label — Photos: 512 MB — and a multiplier, so 3 x 4.7 GB counts as three discs. A bare number with no unit is read as bytes, blank lines are skipped, and lines beginning with # or // are ignored.

The awkward part of file size arithmetic is what KB, MB and GB actually mean, and that is where this tool is explicit rather than quiet. The 1000 / 1024 switch decides how those SI-style units are read: drive labels and most operating systems now use 1000, while Windows and RAM figures use 1024. KiB, MiB and GiB stay 1024-based whichever way the switch is set, because that is what the IEC units mean. Only the base you picked is shown at a time — there is no side-by-side column — but a note under the table records which reading produced it, and that note is copied along with the rows, so a figure pasted into a spreadsheet still says how it was counted.

Two things this calculator refuses to do are worth knowing before you type. It converts numbers you type — there is no file input, so it cannot look at a folder or a drive and report what is inside; read the sizes from your file manager and paste the list in. And the arithmetic uses ordinary JavaScript numbers, which stop holding every whole value above 2^53 bytes, roughly 9 PB. Past that the byte count is prefixed with ≈ instead of printing digits that would not be true. Anything larger than exabytes, such as ZB, is refused by name, and a line that is not a recognisable size is reported with its line number.

One quirk in Show total in is worth naming: that list offers decimal labels only, B through PB. Choose GB while the 1024 setting is active and the total is divided by 1024 three times yet still labelled GB, so the number is really gibibytes wearing an SI name. Leaving the field on auto avoids that, because auto switches to KiB, MiB and GiB labels as soon as the 1024 base is selected. All of this happens inside the page: no figures are sent to a server, none are stored between visits, and the tool keeps working with the network switched off.

How to use it

  1. Decide what KB, MB and GB mean. Pick 1000 for drive labels and most operating systems, or 1024 for Windows and memory figures. KiB, MiB and GiB ignore the switch and stay 1024-based.
  2. Type the sizes, one per line. Each line takes an optional label, a number, a unit and an optional multiplier — Videos: 3 x 4.7 GB. A number with no unit is counted as bytes.
  3. Or leave the box empty to convert one value. With no lines typed, the Value and Unit fields are used on their own, which is the quicker path for a single bytes-to-GB conversion.
  4. Choose the unit for the total. Auto picks a readable unit and labels it correctly for the base you chose. A fixed unit forces every row into the same scale for comparison.

Processing & privacy

Runs on your device. Your file is processed directly in this browser.

Common use cases

Checking a set of files against an upload limit

Paste the individual sizes and read the total before starting a transfer that would otherwise fail somewhere near the end.

Explaining why a 1 TB drive reports 931 GB

Enter 1 TB at the 1000 base to get 1,000,000,000,000 bytes, then paste those digits back with 1024 selected — a bare number ignores the base — and the row reads 931.3 GiB, the operating system's figure.

Sizing a backup set with repeats

Multipliers keep the list short — 3 x 4.7 GB for a spindle of discs, or 30 x 250 MB for a month of nightly dumps.

Reading a hardware spec written in bits

A 512 Mbit flash chip is 64 MB; typing the bit figure converts it, because bit units are divided by eight before anything is totalled.

Questions

Why does my 1 TB drive show up as 931 GB?
The drive is labelled with 1,000,000,000,000 bytes and the operating system divides by 1024 three times. Nothing is missing — the two conventions disagree. This page shows one convention per run, so read the byte count with 1000 selected and enter that plain number again with 1024 to see the smaller figure.
Which units can I type?
B and bytes, KB through EB, KiB through EiB, the bit forms such as bits, Mbit and Gibit, and the spelled-out names — kilobyte, mebibyte, gigabytes. The typed box accepts more units than the Unit dropdown lists.
Do the figures I type leave this tab?
No. Parsing and arithmetic happen in this browser tab, so the figures you type stay in the page, nothing is stored between visits, and the tool still works with no connection.
Can it measure a file or a folder for me?
No. It has no file input and never sees your files. It converts and totals the numbers you supply, so take the sizes from your file manager or terminal and paste them in, one per line.
Will it tell me how long a transfer takes?
No. This handles sizes only, not throughput or time. Converting Mbps against MB/s is the job of the Data Rate Converter instead.
Why is a very large total marked with ≈?
Above 2^53 bytes, about 9 PB, a JavaScript number can no longer represent every whole value. Rather than print digits that are slightly wrong, the count is flagged as approximate.

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