Why does my 1 TB drive show about 931 GB?

Your drive label and Windows can count the same bytes in different-sized units. That's how a 1 TB drive can show about 931 GB without any bytes going missing.

FluffyBench · 4 min read · Reviewed October 15, 2026

Why can the same drive have two size readings?

A byte is a small unit of digital data. Picture your drive's bytes as a pile of coins: counting with a bigger scoop gives you a smaller tally for the same pile.

One unchanged pile of byte tokens branches into two scoops: KB holds 1,000 bytes and KiB holds 1,024 bytes. The bigger scoop takes fewer scoops to count the pile. — The scoop sizes change; the pile doesn't. Tokens illustrate the idea, not individual bytes. Sources and method

Drive labels use decimal units, built in steps of a thousand. Windows File Explorer counts in binary units, built in steps of 1,024, and still labels its readings KB, MB and GB. That's why the letters on their own can be confusing: the label and the screen can mean different-sized scoops.

How does 1 TB become about 931 GB in Windows?

A 1 TB label means 1,000,000,000,000 bytes. Count that capacity in binary gigabytes, called gibibytes (GiB), and you get 931.32 GiB—displayed as about 931 GB in Windows.

Crops of the Samsung label show 1TB and 1GB=1,000,000,000 bytes. Calculated conversion: 1 TB is 1,000,000,000,000 bytes, divided by 1,073,741,824 bytes per GiB, giving 931.32 GiB, displayed as about 931 GB in Windows. — This is arithmetic from the printed capacity, not a measurement of the photographed drive. · Photo: Dinkun Chen, Creative Commons Attribution-ShareAlike 4.0 International, via Wikimedia Commons.

The label's fine print makes its meaning clear: 1 GB is 1,000,000,000 bytes. A GiB holds more bytes, so you need fewer of them to count the drive.

Is 931 GB a sign of missing storage?

The 931 GB reading fits the unit conversion. If you're checking a drive's capacity, compare its total capacity before looking at how much room is free.

Three checks: find total capacity in bytes; compare the label and total in one unit; distinguish total from free space. A schematic total-capacity bar contains files, formatting and system use, and free space. — Free space is what's left after files, formatting and system use take their share. The space split is illustrative.

Doing it in FluffyBench: convert a drive's capacity

FluffyBench's Data size converter translates the number on a drive label into the unit you want to compare. Here's the 1 TB conversion, from the unit pickers to the result you can copy.

Step 1. From is the unit on your drive label; To is the unit you want to compare.
1. Open From to choose the label's unit.
2. Open To to choose the comparison unit.
Step 2. Choose TB under From. Choosing a unit closes the picker.
1. Choose Terabyte (TB).
Step 3. Open To and choose GiB for Windows' binary count.
1. Choose Gibibyte (GiB).
Step 4. Enter 1 in Input value for a 1 TB label.
1. Type 1; the result updates as you type.
Step 5. Read the result as about 931.32 GiB. Copy puts the result number on your clipboard.
1. This is the same capacity in GiB.
2. Copy copies the result number.

Need FluffyBench's Data size converter to compare a drive label with Windows?

Data size

Why do decimal and binary units grow farther apart?

Each step up multiplies decimal units by a thousand and binary units by 1,024. That small difference builds up, so the larger unit pairs are farther apart.

Four paired bars compare decimal and binary unit sizes: KB/KiB 2.40%, MB/MiB 4.86%, GB/GiB 7.37%, TB/TiB 9.95%. Each row uses its own scale; the binary unit is larger. — The binary unit is 2.40%, 4.86%, 7.37% and 9.95% larger at each pair. These compare unit sizes, not lost storage.

How we reviewed

Reviewed October 15, 2026

Byte counts, the 1 TB conversion and unit-size gaps come from the measurement record, the Data size converter's checked conversion records. The conversion diagram divides the label's stated capacity by the byte size of a GiB; the result is rounded to two decimal places and to a whole number for the Windows label. The Samsung SSD photo supplies the printed 1 TB and decimal GB definition; it is not a measurement of that drive. NIST supplies the binary names and their sizes, approved by the IEC in 1998. Apple's storage page explains decimal storage labels; Raymond Chen's 2009 note explains Explorer's use of KB/GB labels for binary counts.

The walkthrough uses FluffyBench's current Data size converter. It updates as the input changes; Copy copies the result number. The diagrams use the checked conversions, not a new drive measurement.

The scoop tokens and capacity allocation are schematic. Unit-size gaps compare each binary unit with the corresponding decimal unit; they aren't percentages of missing capacity. The label details are crops of the credited photograph.

Image credits

Samsung SATA SSD 870 QVO 1TB rear label — Dinkun Chen. Creative Commons Attribution-ShareAlike 4.0 International. Cropped around the capacity rating and decimal-byte fine print from native source pixels, resized to 1,400 pixels wide, and converted to WebP.