Mbps vs MB/s: why your 100 Mbps internet downloads at 12 MB/s
You pay for 100 Mbps, start a big download and see 11.8 MB/s. Nothing is wrong: the two numbers use different units, and the small letter makes an eightfold difference.
Plan speed vs download speed and time
Best case, before overhead, with nothing else using the line. Real downloads are often 5 to 15% slower, and much slower if the server or Wi-Fi is the limit.
| Plan | Best MB/s | 1 GB file | 50 GB game |
|---|---|---|---|
| 10 Mbps | 1.25 MB/s | about 13 min | about 11 hours |
| 36 Mbps | 4.5 MB/s | about 4 min | about 3 hours |
| 67 Mbps | 8.4 MB/s | about 2 min | about 1 h 40 min |
| 100 Mbps | 12.5 MB/s | about 80 s | about 67 min |
| 150 Mbps | 18.75 MB/s | about 53 s | about 44 min |
| 500 Mbps | 62.5 MB/s | about 16 s | about 13 min |
| 900 Mbps | 112.5 MB/s | about 9 s | about 7.5 min |
| 1 Gbps (1,000 Mbps) | 125 MB/s | about 8 s | about 7 min |
The sum: seconds = GB × 8,000 ÷ Mbps. Or skip the sums: the unit converter in Data rate mode turns Mbps into MB/s (and MiB/s) and has a download-time box for a photo, film, game or backup, at full speed and with typical overhead. Its Data size mode covers bytes, KB, MB, GB and TB and their binary cousins (KiB, MiB, GiB), so you can check the GB vs GiB gap below.
GB vs GiB, the other trap
A gigabyte (GB) is 1,000,000,000 bytes, while a gibibyte (GiB) is 1,073,741,824 bytes (1024 × 1024 × 1024). Windows labels GiB as "GB", so a 100 GB download can show as about 93 "GB" on disk. The same 7% gap is why a new 1 TB drive shows about 931 GB.
Bandwidth, throughput, ping, jitter
| Term | Meaning | What it affects |
|---|---|---|
| Bandwidth | The most the connection can carry, what the plan is sold as | Big downloads, several 4K streams at once |
| Throughput | What you actually get at this moment | The number a speed test or download shows |
| Latency (ping) | Round-trip time for one tiny message, in ms | Games, video calls, how snappy pages feel |
| Jitter | How much the ping varies from moment to moment | Choppy calls and rubber-banding in games |
| Packet loss | Messages that never arrive and must be resent | Freezes and drops even on a fast plan |
A 1 Gbps line with 60 ms ping and jitter feels worse for gaming than a 70 Mbps line with a steady 12 ms. Wirebook explains the difference with a picture: What is bandwidth? and What is throughput?
Why the speed test is lower than your plan
- Wi-Fi: the biggest cause. Test with a cable to the router; if that is close to the plan, the line is fine and Wi-Fi is the limit. See 2.4 vs 5 GHz and Wi-Fi generations.
- The device: an older laptop, a 100 Mbps Ethernet port or a USB adapter can cap the speed.
- Other users: a console update, cloud backup or video stream in another room shares the same line.
- "Up to" speeds and busy evenings: plans are sold as typical or "up to" figures. In the UK, providers signed up to Ofcom's broadband speeds code give you a minimum guaranteed speed when you sign up, with a route to leave if they can't fix speeds below it.
- VPN or the far server: a VPN or a slow download server limits throughput regardless of your line.
How much speed do you need?
Roughly: HD streaming about 5 Mbps, 4K about 15 to 25 Mbps per stream, a video call 2 to 4 Mbps each way, online games under 5 Mbps but with low ping. Add up what runs at the same time and leave headroom; upload speed matters too if anyone sends large files or streams.
Related
Speedtest vs Fast.com vs your provider · Broadband speed calculator: what your household needs · How much broadband speed do I need? · Upload time by file size and speed · Why videos start blurry, then sharpen · Video keeps buffering · How long a 100 GB game should take · Upload speed for video calls · Ethernet cable categories · What is a good ping, jitter and packet loss? · Lag when someone downloads (bufferbloat) · Wi-Fi keeps disconnecting: causes and fixes · Wi-Fi 6, 6E and 7 names explained · Best Wi-Fi channel (1, 6, 11 and 5 GHz) · 2.4 GHz vs 5 GHz Wi-Fi · Mesh Wi-Fi backhaul and placement
Questions
Is Mbps the same as MB/s?
No. Mbps is megabits per second and MB/s is megabytes per second. There are 8 bits in a byte, so divide Mbps by 8 to get MB/s.
What is 100 Mbps in MB/s?
12.5 MB/s at best, and usually about 11 to 12 MB/s in a real download because of protocol overhead.
How long does it take to download 50 GB on 100 Mbps?
About 67 minutes at best: 50 × 8,000 ÷ 100 = 4,000 seconds. Expect a little longer in practice.
What is the difference between bandwidth and throughput?
Bandwidth is the most a connection can carry. Throughput is how much actually gets through at a given moment, which is what a speed test measures.
Why is my speed test slower than my broadband plan?
Usually Wi-Fi. Test with an Ethernet cable to the router; if that matches the plan, improve the Wi-Fi. Otherwise check other devices using the line, the device itself, a VPN, and busy evening times.
Published · updated .