GB to MB Converter

The short answer: 1 GB = 1,000 MB

On the decimal scale, the one used on the box of every hard drive, SSD, phone and memory card, 1 GB = 1,000 MB, 1 MB = 1,000 KB and 1 KB = 1,000 bytes. The prefixes are the ordinary metric ones, so a gigabyte is 10 to the power of 9 bytes.

On the binary scale, 1 GiB = 1,024 MiB. The names are different on purpose: GiB is a gibibyte and MiB is a mebibyte, and they are powers of 2 rather than powers of 10. 1 GiB = 1,073,741,824 bytes, which is 7.4% more than a decimal GB.

Both scales are used in real life, and the same file can be described with either. That is the whole reason people argue about how many MB are in a GB. The converter above sidesteps the argument by showing you both numbers side by side, plus the raw byte count that nobody can disagree about.

One practical warning: when a file is described as "1 GB" by a download site, it usually means 1,000,000,000 bytes, but when Windows shows that same file as 953 MB it is dividing by 1,048,576. Neither is lying. The confusion is entirely in the prefixes, which is why the binary units got their own names. KiB, MiB, GiB, TiB, in 1998.

Decimal vs binary: why both exist

Storage hardware is addressed in powers of two, so engineers naturally counted in 1,024s. Memory chips do come in powers of two, and the operating system has to speak that language. But the metric prefixes kilo, mega and giga have always meant powers of ten, and that is what manufacturers use when they print a capacity on a box.

The result is that a drive sold as 1 TB holds 1,000,000,000,000 bytes. Divide that by 1,024 four times and you get 931.3 GiB, which an older Windows install will cheerfully label "931 GB". Nothing was lost in formatting, the same bytes are all there, but two different units are wearing the same three letters.

In 1998 the International Electrotechnical Commission standardised the binary prefixes (KiB, MiB, GiB, TiB) precisely to end this confusion, and the NIST reference on binary prefixes explains the rule. The IEC maintains the standard itself. In practice, marketing kept using the decimal prefixes and operating systems kept using the binary maths, so the gap is still with us.

GB to MB conversion table

The table shows the same sizes in both systems. The binary column is what Windows-style tools will report; the decimal column is what the drive label says.

Read the last row carefully: a 1 TB drive is 1,000,000 MB, which is 953,674 MiB. That is why "1 TB" and "931 GB" describe the same drive.

Worked example: the 128 GB phone that shows 119 GB

You buy a phone advertised as 128 GB. Plug it into a Windows PC and it reports 119 GB. Here is the whole calculation:

• Advertised capacity: 128 GB = 128,000,000,000 bytes
• Windows divides by 1,073,741,824: 128,000,000,000 ÷ 1,073,741,824 = 119.2 GiB
• Windows then labels those GiB as "GB", so it prints 119 GB

Nothing is missing, 119.2 GiB and 128.0 GB are the same number of bytes. The apparent 9 GB shortfall is 6.9% of the drive, which is almost exactly the 7.4% gap between a decimal GB and a GiB after rounding.

The same maths explains a 1 TB drive showing 931 GB, a 512 GB SSD showing 476 GB, and a 64 GB memory card showing 59.6 GB. If you want the number the manufacturer used, multiply the reported figure by 1.0737. If you want the number Windows will show, divide the advertised figure by 1.0737.

Worked example: what fits in 1 GB

One gigabyte is 1,000 MB, which is 8,000 megabits, that second number matters when you are estimating download times. In everyday terms, 1 GB holds roughly:

• 250 phone photos at 4 MB each (modern phones shoot 3 to 6 MB, so expect 170 to 330)
• 250 songs at 4 MB each in a compressed format, or 60 songs as uncompressed audio
• 20 minutes of 1080p video at about 50 MB per minute
• 4 minutes of 4K video at roughly 250 MB per minute
• About 40 minutes of video calling at 0.5 MB per second, or 2.5 hours at low quality

Run the numbers the other way and a 5 GB data plan is 5,000 MB, which is about 1.5 hours of 4K streaming at 7 GB per hour, or roughly 10 hours of standard-definition video. The calculator's "how much of a 128 GB phone" line tells you the same thing as a share of a typical device.

Which unit should you use?

For buying storage, use the decimal units, because that is what the label, the packaging and the spec sheet use. A "1 TB" drive is 1,000 GB and that is the number you compare against price.

For anything the operating system reports, expect binary units, even when the letters say otherwise. When a download manager says a file is 4.38 GB but the store page said 4.7 GB, you are looking at the same file in two systems, not a different file.

For networking and data plans, everything is decimal: a 5 GB plan is 5,000 MB, and a 100 Mbps connection moves 12.5 MB per second. Mixing the two systems is the single most common source of "where did my space go" confusion, so it pays to pick the decimal figure when you are comparing a price and the binary figure when you are checking a Windows dialog box.

One last shortcut worth memorising: to go from advertised GB to the number Windows shows, multiply by 0.931. To go the other way, multiply by 1.074.