Mbps vs. MB/s vs. Gbps: Stop Confusing Bits and Bytes
Speed tests report megabits (Mbps) while your file manager shows megabytes (MB/s), and the two differ by a factor of eight. Once you internalize the ÷8 conversion, a lot of "my connection is slower than promised" mysteries disappear.
Few things in home networking cause more confusion than units. Your ISP advertises a plan in one measure, a speed test confirms it in the same measure, and then you copy a file and the number your computer shows looks eight times smaller. Nothing is broken — you are simply reading two different units. This guide clears it up for good.
Bits vs. bytes: the eight-to-one rule
The entire confusion comes down to a single fact: 8 bits = 1 byte.
A bit is the smallest unit of digital data, a single 1 or 0. A byte is a group of 8 bits. Networking has traditionally measured speed in bits per second, because data travels across a wire one bit at a time. Storage and files, on the other hand, are measured in bytes, because that is how memory and disks are organized.
The tell is in the capitalization. A lowercase b means bits; an uppercase B means bytes:
- Mbps = megabits per second (network speed — ISPs, speed tests)
- MB/s = megabytes per second (file transfers — your file manager)
- Gbps = gigabits per second (fast links: gigabit Ethernet, "gig" internet)
Note: Read the case carefully. "100 Mb" and "100 MB" are eight times apart. Marketing almost always uses the bigger-sounding bits (Mbps); file tools almost always use bytes (MB/s).
The conversion: divide by eight
To go from a network speed in megabits to a file-transfer rate in megabytes, divide by 8:
Megabytes per second = Megabits per second ÷ 8
So a 100 Mbps connection can, in theory, move data at 100 ÷ 8 = 12.5 MB/s. A gigabit (1000 Mbps) link works out to 1000 ÷ 8 = 125 MB/s. Going the other way, multiply by 8: a download running at 20 MB/s is using 160 Mbps of your connection.
What "gigabit" actually delivers
Here is where realistic expectations matter. The clean theoretical numbers above assume every bit carries your file and nothing else. In practice, some of the link is consumed by overhead — the packaging around your data.
Network data is wrapped in headers for protocols like TCP/IP and Ethernet. These headers are necessary for the data to route, arrive in order, and be verified, but they are not part of your file. They typically eat a few percent of the raw capacity. So a gigabit connection whose theoretical ceiling is 125 MB/s realistically delivers about 112–118 MB/s in a healthy wired transfer. That is not a defect; it is the normal cost of moving data reliably.
This is why a large file copy over gigabit Ethernet landing around 113 MB/s is a sign of a perfectly healthy network, not an underperforming one. If you are seeing that, your wiring, switch, and NICs are all doing their job. For what can drag it below that, see why NAS transfers run slow and our overview of Ethernet vs. Wi-Fi speed.
Conversion table for common link speeds
| Link speed (Mbps) | Theoretical MB/s (÷8) | Realistic MB/s (after overhead) | Common context |
|---|---|---|---|
| 25 Mbps | 3.1 MB/s | ~2.7 MB/s | Basic broadband |
| 100 Mbps | 12.5 MB/s | ~11 MB/s | Fast Ethernet; entry broadband |
| 300 Mbps | 37.5 MB/s | ~33 MB/s | Good Wi-Fi; mid-tier internet |
| 1000 Mbps (1 Gbps) | 125 MB/s | ~112–118 MB/s | Gigabit Ethernet; "gig" internet |
| 2500 Mbps (2.5 Gbps) | 312.5 MB/s | ~275–295 MB/s | Multi-gig home networking |
| 10000 Mbps (10 Gbps) | 1250 MB/s | ~1100–1180 MB/s | High-end NAS / server links |
If those higher rows interest you, our guide to multi-gig home networking covers what it takes to actually reach 2.5G and beyond.
Worked examples
Example 1: "Why is my download only 12 MB/s on my 100 Mbps plan?" It is not slow — it is exactly right. 100 Mbps ÷ 8 = 12.5 MB/s theoretical, so ~11–12 MB/s in practice is your plan working as intended. The plan is in bits; the download counter is in bytes.
Example 2: How long to download a 4 GB game on gigabit? First convert the file: 4 GB = 4096 MB. At a realistic 115 MB/s, that is 4096 ÷ 115 ≈ 36 seconds — assuming the server on the other end can send that fast, which is often the real limit.
Example 3: Will a 4K stream fit on a 25 Mbps connection? A 4K stream needs roughly 25 Mbps at the high end. That is 25 Mbps ÷ 8 ≈ 3.1 MB/s of actual data. Your 25 Mbps plan can just cover a single 4K stream, but leaves little room for anything else on the network at the same time.
Tip: When comparing a speed test to a file copy, convert one to match the other before you panic. Multiply the file-copy MB/s by 8 to compare it against a speed-test Mbps figure, and the numbers usually line up.
The habit worth building
Whenever you see a network number, glance at the units first. Lowercase b, divide by eight to picture the file-copy rate. Uppercase B, multiply by eight to picture the link speed. That one reflex resolves the majority of "I'm not getting the speed I pay for" complaints, which are really just bits being mistaken for bytes.
Units are not a technicality here — they are the whole story. Get them straight, and the rest of your network's numbers finally start making sense. From there, guides like throughput, latency, and jitter build on the same foundation.