GB to MB Converter

gigabytes to megabytes — quick reference

The formula

A gigabyte is exactly one thousand megabytes in decimal SI, so this is one multiplication and the constant carries no rounding of its own. The same factor of a thousand joins every rung of the decimal ladder, from kilobytes up through terabytes, which is why the whole system amounts to a decimal point moving three places at a time.

The binary answer, when you need it, pivots through bytes rather than through a second rounded factor. Multiply gigabytes by 1,000,000,000 to get bytes, then divide by 1,048,576 for mebibytes or by 1,073,741,824 for gibibytes. Doing it in one pass through bytes is what stops small errors compounding once you get to the terabyte end of the scale.

MB = GB × 1,000
bytes = GB × 1,000,000,000
MiB = GB × 1,000,000,000 ÷ 1,048,576
MB/s = Mbps ÷ 8

Worked example with the default value: 5 × 1,000 = 5,000 MB. Set against real limits, that is 200 attachments at a 25 MB cap, about 16 app updates at 300 MB each, or roughly 167 MB a day across a 30-day billing cycle. The same 5 GB in binary units is 5,000,000,000 ÷ 1,073,741,824 = 4.66 GiB, or 4,768 MiB, which Windows would label 4.66 GB. The byte count never moved; only the divisor did.

Scaling up follows the identical single step. A 64 GB phone holds 64,000 MB, a 128 GB one holds 128,000 MB, and a 2 TB drive holds 2,000 GB or 2,000,000 MB. Where the arithmetic stops being trivial is when a device reports in binary while still writing GB: that 64 GB phone reads as 59.60 GB in Windows, because 64,000,000,000 ÷ 1,073,741,824 = 59.60. The 4.40 GB difference is purely a change of ruler, and it sits on top of whatever the operating system and preinstalled apps genuinely occupy.

The unit next door is the megabit, and it produces eightfold errors rather than seven percent ones. Speeds are sold in megabits per second, files are measured in megabytes, and eight bits make a byte, so divide the advertised speed by eight before comparing it to a file size. At 100 Mbps that is 12.5 MB per second and a 5 GB download takes 400 seconds at best. At 25 Mbps it is 3.125 MB per second and the same download needs 1,600 seconds, a little under 27 minutes. Carriers count your data allowance in bytes, though, so the plan and the file agree even when the speed does not.

How to use the gb to mb converter

Gigabytes are how storage and connectivity get sold: a 5 GB monthly plan, a 128 GB phone, a 2 TB external drive, a 50 GB game. Almost everything you then measure against them is quoted in megabytes. Mail servers cap attachments at 25 MB. App updates arrive at 80 MB or 300 MB. A usage screen counts today in megabytes. A hotel or airline captive portal doles out a few hundred megabytes at a time. This converter multiplies gigabytes by 1,000 so both sides of that comparison sit in the same unit and the answer is a whole number you can hold in your head. Swap runs it the other way when a file listing hands you gigabytes and the limit you are checking is written in megabytes.

The most common reason to do this conversion is budgeting a mobile data allowance, and the useful move is turning the monthly figure into a daily one. A 5 GB plan is 5,000 MB, which across a 30-day cycle is about 167 MB a day — a number you can genuinely check against a phone usage screen at lunchtime. A 20 GB plan gives you 20,000 MB, roughly 667 MB a day. A 100 GB plan is 100,000 MB, about 3,333 MB a day. The daily figure matters because allowances are consumed unevenly and the monthly number tells you nothing until the month is nearly over. Carriers define the gigabyte decimally, so these are the real numbers behind the bill rather than an approximation of them.

The multiplier is 1,000 because this converter uses the decimal SI definition: 1 GB = 1,000 MB = 1,000,000 KB = 1,000,000,000 bytes. That is what carriers, drive makers and spec sheets mean when they print GB. The binary units are a separate system with separate names, standardised by the IEC as kibibyte, mebibyte and gibibyte and written KiB, MiB and GiB, where 1 GiB = 1,024 MiB = 1,073,741,824 bytes. IEC 80000-13 keeps the two apart by reserving the plain SI prefixes for powers of a thousand. If you genuinely need the binary answer, 5 GB is 4,768 MiB rather than 5,000 MB — and it is worth writing the unit out in full so the next person reading your spreadsheet knows which one you meant.

One more unit lives next door and is easy to trip over. Storage counts bytes; connection speeds count bits, and there are eight bits to a byte. A line sold as 100 Mbps therefore moves at most 12.5 MB per second, so a 5 GB download needs 5,000 ÷ 12.5 = 400 seconds, a little under seven minutes, at the full line rate. Real transfers run slower because protocol overhead, server-side limits, shared capacity and Wi-Fi all take a cut, which makes the arithmetic a floor on time rather than a promise. The capital B in MB and the lower-case b in Mb are doing all the work in that sentence, which is why an eightfold surprise is so common when someone times a download against their advertised speed.

Every gigabytes value, worked out

73 common gigabytes figures each get their own page, with the answer, the arithmetic, what rounding costs, and the nearest real-world reference point on the scale.

Frequently asked questions