Who needs this?
Anyone who has stared at a progress bar and wondered if the plan lives up to its ad:
- GamersA 60 GB update drops the night before a match. Is it a 10-minute wait or a 2-hour one?
- Anyone shopping for internetThe jump from 300 to 1,000 Mbps costs more each month. What does it actually save on a typical download?
- Remote workersUploading a big presentation or a screen recording on an upload speed that's a fraction of the download speed.
- Photographers and video editorsSending a day's shoot to a client or a cloud backup and planning around the wait.
- IT and network techsChecking whether a transfer rate is normal for the link or a sign that something is wrong.
- HouseholdsFour people streaming, gaming and backing up phones on one shared connection.
Bits, bytes and the factor of 8
A bit is a single 1 or 0. A byte is 8 bits. Networks count bits, because a line sends them one after another; storage counts bytes. The abbreviations differ only in the case of one letter:
- Mb and Mbps (lowercase b) mean megabits and megabits per second. This is what your provider sells.
- MB and MB/s (capital B) mean megabytes and megabytes per second. This is what file sizes, browsers and game launchers show.
- Divide Mbps by 8 to get MB/s. A 100 Mbps plan tops out at 12.5 MB/s, and a 1 Gbps (1,000 Mbps) plan at 125 MB/s.
Think of a moving truck rated in shoeboxes per hour while your stuff is packed in crates that each hold 8 shoeboxes. "800 per hour" sounds fast until you realize it's 100 crates. Neither number is a lie; they're counting different boxes.
The figure shows one 4 GB file at five common speeds, drawn to scale (the times are at full speed, with no overhead).
The minutes you save shrink fast as speed climbs. Going from 10 to 100 Mbps saves 48 minutes on this file. Going from 300 to 1,000 Mbps saves 75 seconds.
Working out a download time, step by step
The math is the same for any file and any line: turn the size into bits, then divide by the speed in bits per second.
- Turn GB into MB
4 GB × 1,000 = 4,000 MB - Multiply by 8 to get megabits
4,000 × 8 = 32,000 Mb - Divide by the speed
32,000 Mb ÷ 100 Mbps = 320 s - Turn seconds into minutes
320 ÷ 60 = 5 min 20 s
That's the best case. The calculator adds a 10% allowance for overhead by default, which brings this one to about 5 min 56 s:
File size: 4 GBInternet speed: 100 MbpsOverhead and slowdowns: 10%
To flip between the two kinds of "per second", use the converter. Type an Mbps figure to see the MB/s it can carry, or the other way round:
If the answer comes out as a decimal number of hours or minutes (1.78 h, say), the time and decimal hours guide shows how to turn it into hours and minutes.
Real situations, worked out
60 GB is 60,000 MB, which is 480,000 megabits. 480,000 ÷ 300 = 1,600 seconds, or 26 min 40 s at full speed. With the 10% allowance it's 1,778 seconds, about 29 min 38 s. Plan on half an hour.
60 GB at 300 Mbps ≈ 27 to 30 minutesFile size: 60 GBInternet speed: 300 MbpsOverhead and slowdowns: 10%
One 2 MB photo is 16 megabits. 16 ÷ 10 = 1.6 seconds, so a single shot feels instant. A batch of 200 photos is 400 MB, or 3,200 megabits: 320 seconds at full speed and about 5 min 56 s with overhead.
1 photo ≈ 1.6 s · 200 photos ≈ 5 to 6 minutes30 MB/s × 8 = 240 Mbps. That's 80% of the advertised 300, which is about what a healthy connection delivers once overhead, Wi-Fi and the server's own limits are counted. If it showed 3 MB/s (24 Mbps), that would be worth a look.
30 MB/s = 240 Mbps, 80% of the planA 56k modem moved at most 56 kilobits per second (0.056 Mbps). 32,000 megabits ÷ 0.056 = 571,429 seconds, which is about 158.7 hours, or 6.6 days of nonstop downloading. At 100 Mbps the same file takes 5 min 20 s.
4 GB at 56 kbps ≈ 6.6 daysDoing it in your head
For a real-world MB/s figure, divide the Mbps by 10. The exact maximum is Mbps ÷ 8, and dividing by 10 builds in a 20% cushion for overhead, which is close to what most home connections actually deliver.
| Plan | Exact maximum (÷ 8) | Quick estimate (÷ 10) | With 10% overhead |
|---|---|---|---|
| 25 Mbps | 3.125 MB/s | 2.5 MB/s | 2.81 MB/s |
| 100 Mbps | 12.5 MB/s | 10 MB/s | 11.25 MB/s |
| 300 Mbps | 37.5 MB/s | 30 MB/s | 33.75 MB/s |
| 500 Mbps | 62.5 MB/s | 50 MB/s | 56.25 MB/s |
| 1,000 Mbps | 125 MB/s | 100 MB/s | 112.5 MB/s |
A gigabyte peg. At full speed, 1 GB takes 8,000 ÷ Mbps seconds. On 100 Mbps that's 80 seconds per GB, so a 60 GB game is about 80 minutes. Scale from there.
Why real downloads run slower
The advertised number covers the line between your home and the provider. A download crosses more than that, and several things take a share:
- Protocol overhead. Every packet carries addressing and error-checking data along with your file, which costs a few percent.
- Wi-Fi. Walls, distance and neighbors' networks often cut throughput well below the plan. A wired connection is the fair test.
- The server. A busy server, or one that caps each user, can be the slowest link no matter how fast your line is.
- Sharing. Everyone in the house shares the plan, and in busy evening hours some networks slow down.
That's why the calculator applies 10% by default. Use 0% for the theoretical best and 25% for crowded Wi-Fi.
Upload is usually the slow lane
Many plans are asymmetric: upload is a fraction of download. Cable plans are the usual example; fiber is often the same speed both ways. The upload number is the one that governs backups, video calls and sending work to clients.
Speed and latency are different things
Bandwidth (Mbps) is how much data moves per second. Latency (ping, in milliseconds) is how long one small message takes to make the round trip. Big downloads care about bandwidth; games and video calls care about latency, so a fast plan with high ping can still feel laggy.
Common mistakes
Reading Mbps as MB/s. A 100 Mbps plan does not download 100 MB every second. It moves 12.5 MB/s at most, so a 1 GB file takes 80 seconds, not 10.
Expecting the full advertised speed over Wi-Fi. Run a speed test on a cable plugged into the router before deciding the provider is short-changing you. Wi-Fi is often the real limit.
Forgetting that GB and GiB differ. Some operating systems report sizes in binary units. A "4 GB" file shown that way is really 4 GiB, or about 4,295 MB, which takes about 5 min 44 s at 100 Mbps instead of 5 min 20 s. The bits, bytes and storage guide explains the two systems.
Using the download speed for an upload. If the plan is 300 down and 20 up, a 1.5 GB video upload takes 10 minutes at full speed, not 40 seconds.
A bit of history
- 1962AT&T's Bell 103 modem carries data over phone lines at 300 bits per second. At that rate, a 4 GB file would take about 3.4 years.
- 1997The first IEEE 802.11 Wi-Fi standard is published, with speeds up to 2 Mbps.
- 1998The ITU approves V.90, the standard for 56k dial-up modems: 56 kbps down, at best.
- 1999The ITU approves its ADSL standard, which let ordinary phone lines carry always-on broadband alongside voice calls.
Speeds have been quoted in bits per second the whole way, which is why the factor of 8 is still with us.
Reference table
Times at full speed, no overhead. Add about 10% for a typical real download.
| File | Size | 25 Mbps | 100 Mbps | 300 Mbps | 1,000 Mbps |
|---|---|---|---|---|---|
| Song | 5 MB | 1.6 s | 0.4 s | 0.1 s | under 0.1 s |
| App update | 100 MB | 32 s | 8 s | 2.7 s | 0.8 s |
| HD TV episode | 1.5 GB | 8 min | 2 min | 40 s | 12 s |
| HD movie | 4 GB | 21 min 20 s | 5 min 20 s | 1 min 47 s | 32 s |
| 4K movie (disc quality) | 50 GB | 4 h 27 min | 1 h 7 min | 22 min 13 s | 6 min 40 s |
| Large game | 60 GB | 5 h 20 min | 1 h 20 min | 26 min 40 s | 8 min |
Questions people ask
How many MB/s is 100 Mbps?
12.5 MB/s at most (100 ÷ 8). In practice expect around 10 to 11 MB/s once overhead is counted.
Why is my download slower than my internet speed?
Partly because of units (Mbps vs MB/s, a factor of 8) and partly because of overhead, Wi-Fi, server limits and other people on the line. Seeing 80 to 90% of the plan, after converting units, is normal.
How long does it take to download 1 GB?
1 GB is 8,000 megabits. At 100 Mbps that's 80 seconds, at 300 Mbps about 27 seconds and at 1,000 Mbps 8 seconds, at full speed.
What upload speed do I need for video calls?
Video calls need far less than most plans offer, but they share the upload with everything else. The FCC's broadband speed guide lists typical needs by activity.