Bits vs bytes is the distinction behind one of technology’s most common confusions: why a “100 Mbps” internet plan never downloads files at 100 megabytes per second. A bit is the smallest unit of digital data, a single 0 or 1. A byte is a group of 8 bits. Internet speeds are advertised in bits per second (Mbps), while file sizes and storage are measured in bytes (MB), so converting between them means dividing or multiplying by 8. Convert any speed or size instantly with our free unit converter.
What a bit is
A bit (binary digit) is the atom of computing: one electrical state, one 0 or 1. Everything digital, your photos, this article, a video call, is ultimately a long stream of bits. Network engineers think in bits because data physically travels across wires and airwaves one bit at a time, serially. Speeds therefore describe how many bits per second the pipe can carry.
What a byte is
A byte is 8 bits grouped together, enough to represent 256 different values (28), which is why one byte historically stores one text character. Software thinks in bytes because files, memory, and storage are organized in byte sized chunks. When your phone says a photo is 4 MB or an app needs 200 MB, those are megabytes, millions of bytes.
The notation matters enormously: a lowercase b means bits, an uppercase B means bytes. Mbps (megabits per second) and MB/s (megabytes per second) differ by a factor of eight, and mixing them up is the root of nearly every speed complaint.
Why ISPs advertise in bits
Two honest reasons and one marketing flavored one. First, networks genuinely operate at the bit level, a 100 Mbps link moves 100 million bits per second across the wire, so bits are the engineer’s natural unit. Second, the convention predates consumer internet: telecom speeds were always quoted in bits per second, from 56k modems onward. Third, and nobody should pretend otherwise, 100 megabits sounds eight times more impressive than 12.5 megabytes, even though they describe the same pipe.
The conversion: divide by 8
The core math is simple: bits ÷ 8 = bytes. A 100 Mbps connection can theoretically move 100 ÷ 8 = 12.5 MB/s. In practice you will see a bit less, around 10 to 11 MB/s, because of protocol overhead: TCP/IP headers, retransmissions, and encryption all consume some of the raw bit rate carrying your actual file.
Worked examples make it concrete:
- Downloading a 1 GB file on 100 Mbps: 1 GB ≈ 8,000 megabits; 8,000 ÷ 100 = ~80 seconds theoretically, realistically 90 to 100 seconds with overhead.
- A 25 Mbps 4K Netflix stream: 25 ÷ 8 = ~3.1 MB/s of actual video data flowing continuously.
- Uploading a 500 MB video on a 20 Mbps upload link: 500 MB = 4,000 megabits; 4,000 ÷ 20 = ~200 seconds, or a little over 3 minutes.
Common size units, decoded
- Kb / Mb / Gb kilobits, megabits, gigabits (network speeds). 1 Mbps = 1,000,000 bits per second.
- KB / MB / GB kilobytes, megabytes, gigabytes (file and storage sizes). 1 MB = 1,000,000 bytes (decimal) in storage marketing.
- KiB / MiB / GiB kibibytes, mebibytes, gibibytes: the binary versions (1 MiB = 1,048,576 bytes) that operating systems often display. This is why a “500 GB” drive shows ~465 GB in Windows.
For a deeper dive into what speed numbers actually mean for streaming, gaming, and video calls, see What Does Mbps Mean? And when text messages seem to have strange length limits, the GSM-7 character set explains why, it is bits and bytes all the way down.
Worked example: where a 256 GB phone’s space actually goes
Start with the storage figure on the box: a phone sold as 256 GB. In bits, that capacity is 256 × 8, which is 2,048 gigabits, a number nobody prints, because storage is the byte’s home territory. Now spend the space. Say the phone holds 3,000 photos at about 4 MB each: 3,000 × 4 MB is 12,000 MB, or 12 GB. Add 20 downloaded films and episodes at roughly 1.5 GB each and that is another 30 GB. The operating system and apps take, for the sake of this example, 40 GB. The running total is 82 GB used of 256, leaving 174 GB free, arithmetic that only works because every figure stayed in bytes. The moment a network number enters the picture, the units must be converted before they are combined: those 12 GB of photos are 96,000 megabits of data, and backing them up on a 20 Mbps upload connection takes 96,000 ÷ 20, which is 4,800 seconds, a full 80 minutes. Mixing the units mid calculation is how people predict a five minute backup and wait over an hour. Convert any of these figures instantly with the free unit converter.
The same division explains the most misread number in home internet: the speed test. A test reporting 92 Mbps and a download manager reporting about 11.5 MB/s are describing the identical flow, because 92 ÷ 8 is 11.5. Neither is rounding down your purchase; they are two dialects of one fact. The practical skill this gives you is prediction. A 500 MB app update on that connection is 4,000 megabits, and 4,000 ÷ 92 is about 43 seconds, which is what the progress bar will show, give or take the usual overhead. Once you can run size in megabits divided by speed in Mbps in your head, download estimates stop being surprises, and the question “is my internet slow?” turns into a comparison between a number you predicted and a number you measured.
There is one more dialect worth recognising, because it explains a mystery from the size list above. Operating systems often count in binary units, a gibibyte is 1,073,741,824 bytes rather than a neat billion, while drive makers label capacity in decimal gigabytes. The phone advertised as 256 GB is honest in decimal; the system reporting about 238 GiB of capacity is describing the same silicon in binary, and 256 billion bytes divided by 1,073,741,824 lands at roughly 238. Nobody has taken 18 GB from you. The gap is purely the two counting systems disagreeing about what the prefix “giga” multiplies, which is why the binary units have their own names, KiB, MiB, GiB, even if everyday speech blurs them together.
The units at a glance
Keep this table nearby and most bits versus bytes confusion never gets started:
| Unit | What it measures | How big it is | Where you meet it |
|---|---|---|---|
| Bit (b) | The smallest unit of data | A single 0 or 1 | Inside every other unit; rarely seen alone |
| Byte (B) | A group of bits | 8 bits | File sizes, storage, memory |
| Megabit (Mb) | Network traffic | 1,000,000 bits | Internet speeds: a 100 Mbps plan |
| Megabyte (MB) | File and storage size | 1,000,000 bytes, or 8 megabits | Downloads, photos, app sizes |
| Gigabit (Gb) | Large network traffic | 1,000 megabits | Gigabit internet sold as 1 Gbps |
| Gibibyte (GiB) | Binary storage size | 1,073,741,824 bytes | The capacity figure your operating system reports |
Common mistakes to avoid
- Comparing Mbps with MB/s directly. They differ by a factor of 8. A download at 12 MB/s on a 100 Mbps plan is the plan working exactly as sold.
- Estimating download time in gigabytes divided by Mbps. Convert the file to megabits first, gigabytes × 8,000, roughly, or your estimate will be eight times too optimistic.
- Blaming a drive maker for the “missing” gigabytes. A 256 GB drive showing about 238 GiB is a units translation, not missing space. Decimal labels and binary reporting describe the same bytes.
- Ignoring upload when the task is sending. Backups, video uploads and cloud sync run on the upload speed, which is usually the smaller number and always quoted in bits too.
- Assuming every “GB” is the same GB. Decimal and binary gigabytes differ by about 7% at the gigabyte scale, and the gap grows with size. Check which one a figure uses before doing arithmetic with it.
- Trusting a single speed figure without its unit. A bare “100” on a settings screen might be Mbps, MB/s or a percentage. The capital or lowercase letter after the number is the whole story.
If you remember one image, make it this: bits are the coins, bytes are the notes. Networks count the flow in coins because that is how data physically travels, one bit after another; files and drives count in notes because that is how data is stored and organised. Converting between them is a single multiplication or division by 8, and nearly every argument about internet speed, storage capacity and download time is, underneath, two people counting in different denominations and both being right. Run the conversion first, by hand, or with the unit converter and the disagreement usually ends before it begins.
A quick drill: four conversions worth practising
Fluency comes from reps, so run these four once and the pattern locks in. First: an 8 GB film file is 8,000 MB, and 8,000 × 8 makes 64,000 megabits. Second: on a 40 Mbps connection, that file takes 64,000 ÷ 40, which is 1,600 seconds, 26 minutes 40 seconds, before overhead. Third: a modest 250 MB photo backup is 2,000 megabits, and on a 10 Mbps upload link it needs 2,000 ÷ 10, or 200 seconds, a little over three minutes. Fourth, reverse direction: a speed test showing 240 Mbps promises downloads of 240 ÷ 8, exactly 30 MB/s at the theoretical ceiling. Notice that every single problem used the same two moves, multiply bytes by 8 to get bits, divide bits by the speed to get seconds, and that no other operation ever appears. That is the whole subject. Everything else in this guide, and most of the confusion in the wild, is those two moves applied carefully or carelessly. Practise them on the next download you start, predict the time before the progress bar does, and you will feel the units click into place permanently.
A second worked example: moving a 50 GB backup across your home network
The same two moves also explain why the same backup crawls on one network and flies on another. Take a 50 GB folder of photos and videos. In the units networks use, that folder is 50,000 MB multiplied by 8, 400,000 megabits of data to move. Across a gigabit Ethernet connection rated at 1,000 Mbps, the theoretical time is 400,000 ÷ 1,000, which is 400 seconds: 6 minutes 40 seconds. Plug the same computer into an older 100 Mbps port instead and the division becomes 400,000 ÷ 100, which is 4,000 seconds, 66 minutes 40 seconds. Nothing about the folder changed; the pipe is simply ten times narrower, so the transfer takes ten times longer, in exact proportion. A Wi-Fi connection rated at 600 Mbps lands between the two at roughly 667 seconds, about 11 minutes, before the usual wireless losses stretch it further. If any of these conversions feels slippery, run the figures through the unit converter and watch the same pattern appear.
This is also why network hardware is sold in bits while the drives it connects are sold in bytes, and why the two numbers on a router box, a 1,000 Mbps port feeding a drive measured in gigabytes, can only be compared after conversion. A backup that looks like it should take “about six minutes” on the box’s headline figure takes over an hour on a slower port, and both predictions are correct for their own hardware. Before blaming a drive or a cable, do the division for the slowest link in the chain: the transfer can never beat the narrowest pipe it crosses, and that pipe is always described in bits per second. Convert first with the unit converter, then measure, the order matters.
Frequently asked questions
Is 100 Mbps fast?
For most households, yes. 100 Mbps (≈12.5 MB/s) comfortably handles multiple 4K streams, video calls, and large downloads simultaneously. It only feels slow if many heavy users share it or the Wi-Fi, not the plan, is the bottleneck.
Why is my download slower than my internet plan?
Three usual suspects: unit confusion (100 Mbps = 12.5 MB/s max, before overhead), Wi-Fi limitations (especially on 2.4 GHz or at distance), and the server you’re downloading from throttling or being congested. Test with a wired connection to isolate your plan’s true speed.
What’s the difference between MB and Mb?
MB (megabyte) is 8 times larger than Mb (megabit). File sizes use MB; internet speeds use Mb/s (usually written Mbps). A 100 Mbps plan delivers at most 12.5 MB/s.
How many bits are in a gigabyte?
8 billion bits (8,000,000,000) in a decimal gigabyte. So moving 1 GB across a 100 Mbps link takes about 80 seconds in theory.
What speed do I actually need?
Rough minimums per simultaneous activity: ~5 Mbps for HD video, ~25 Mbps for 4K video, ~3 to 10 Mbps for video calls, ~20+ Mbps for responsive online gaming (where latency matters more than bandwidth). Add them up for your household’s concurrent use.