Bandwidth Calculator
Convert between bandwidth units like Mbps, Gbps, MB/s and estimate download times. Includes a common file sizes reference table.
Internet speeds are measured in bits per second (Mbps), but file sizes are measured in bytes (MB). This difference confuses many people - a 100 Mbps connection downloads at 12.5 MB/s, not 100 MB/s. This calculator converts between all common bandwidth units and estimates download times for different file sizes at your connection speed. All calculations run in your browser.
About Bandwidth Calculator
Bits vs Bytes - The Key Difference
One byte equals 8 bits. ISPs advertise speeds in bits per second (using a lowercase 'b'), while operating systems show file sizes and download speeds in bytes (uppercase 'B'). This 8x difference is the most common source of confusion.
| Unit | Symbol | Equals | Used By |
|---|---|---|---|
| Kilobits per second | Kbps | 1,000 bits/s | Legacy connections, audio streaming |
| Megabits per second | Mbps | 1,000 Kbps | ISP plans, speed tests, WiFi specs |
| Gigabits per second | Gbps | 1,000 Mbps | Ethernet, fibre, data centre links |
| Kilobytes per second | KB/s | 8 Kbps | Slow download progress bars |
| Megabytes per second | MB/s | 8 Mbps | File downloads, disk throughput |
| Gigabytes per second | GB/s | 8 Gbps | SSD benchmarks, memory bandwidth |
When your ISP sells you a "100 Mbps" plan, your maximum download speed in your browser or file manager is 100 / 8 = 12.5 MB/s. In practice, overhead reduces this to roughly 11-12 MB/s.
Download Time Estimates
The calculator shows estimated download times for common file sizes at your chosen speed.
| File Type | Typical Size | At 50 Mbps | At 100 Mbps | At 1 Gbps |
|---|---|---|---|---|
| Email (text) | 50 KB | Instant | Instant | Instant |
| MP3 song | 5 MB | 0.8 sec | 0.4 sec | 0.04 sec |
| Photo (high-res) | 15 MB | 2.4 sec | 1.2 sec | 0.12 sec |
| HD movie (1080p) | 4 GB | 10.7 min | 5.3 min | 32 sec |
| 4K movie | 15 GB | 40 min | 20 min | 2 min |
| Game download | 80 GB | 3.6 hours | 1.8 hours | 10.7 min |
| Full backup | 256 GB | 11.4 hours | 5.7 hours | 34 min |
These are theoretical best-case times. Real-world downloads are typically 10-30% slower due to protocol overhead (TCP headers, encryption), server-side speed limits, network congestion, and WiFi signal quality.
Common Internet Connection Speeds
| Connection Type | Typical Download Speed | Typical Upload Speed |
|---|---|---|
| 3G mobile | 1-5 Mbps | 0.5-2 Mbps |
| 4G LTE mobile | 20-100 Mbps | 5-30 Mbps |
| 5G mobile | 100-1000 Mbps | 50-200 Mbps |
| ADSL broadband | 5-24 Mbps | 1-3 Mbps |
| Cable broadband | 50-500 Mbps | 5-50 Mbps |
| FTTP fibre | 100-1000 Mbps | 100-1000 Mbps |
| WiFi 5 (802.11ac) | Up to 3.5 Gbps (theoretical) | Same |
| WiFi 6 (802.11ax) | Up to 9.6 Gbps (theoretical) | Same |
| Ethernet (Cat 5e) | 1 Gbps | 1 Gbps |
| Ethernet (Cat 6a) | 10 Gbps | 10 Gbps |
SI Units vs Binary Units
Networking uses SI (base-10) prefixes where 1 Megabit = 1,000,000 bits. Storage sometimes uses binary (base-2) prefixes where 1 Mebibyte (MiB) = 1,048,576 bytes. This tool uses SI units, which is the standard for bandwidth.
| SI (Networking) | Value | Binary (Storage) | Value |
|---|---|---|---|
| 1 KB | 1,000 bytes | 1 KiB | 1,024 bytes |
| 1 MB | 1,000,000 bytes | 1 MiB | 1,048,576 bytes |
| 1 GB | 1,000,000,000 bytes | 1 GiB | 1,073,741,824 bytes |
| 1 TB | 1,000,000,000,000 bytes | 1 TiB | 1,099,511,627,776 bytes |
This is why a "500 GB" hard drive shows as roughly 465 GiB in your operating system. The drive manufacturer uses SI (500 x 10^9 bytes), while your OS reports in binary (dividing by 1024^3).
Bandwidth Requirements for Streaming
| Service | Quality | Recommended Speed |
|---|---|---|
| Netflix | SD (480p) | 3 Mbps |
| Netflix | HD (1080p) | 5 Mbps |
| Netflix | 4K Ultra HD | 25 Mbps |
| YouTube | 4K | 20 Mbps |
| Zoom video call | HD (1080p) | 3.8 Mbps up + down |
| Online gaming | Varies | 3-10 Mbps (latency matters more than bandwidth) |
| Spotify audio | High quality | 0.32 Mbps (320 Kbps) |
These are per-stream requirements. A household with 4 simultaneous HD streams needs at least 20 Mbps of actual throughput. Netflix's published minimums are 3 Mbps for SD, 5 Mbps for HD, and 15 Mbps for a single 4K Ultra HD stream, though 25 Mbps gives a more comfortable buffer for 4K HDR content.
How Does This Calculator Work?
Every input is converted to a canonical value in bits per second (bps), then divided by the target unit's bps equivalent. Download time is the file size in bits divided by the connection speed in bps, or equivalently the file size in bytes divided by the speed in B/s.
Worked example: A 4 GB HD movie on a 100 Mbps connection. 4 GB = 4,000,000,000 bytes = 32,000,000,000 bits. 100 Mbps = 100,000,000 bits per second. Time = 32,000,000,000 / 100,000,000 = 320 seconds, or 5 minutes 20 seconds. The calculator rounds to 5.3 minutes. Add roughly 10-30% for real-world overhead, so expect closer to 6-7 minutes in practice.
A second example: you want to send a 50 MB photo over a 4G connection averaging 25 Mbps upload. 50 MB = 400 Mb. 400 / 25 = 16 seconds at the theoretical peak. Mobile radio overhead and handoffs typically push this to 20-25 seconds in practice.
How Fast Is UK and US Broadband in 2026?
The UK's average maximum download speed reached 285 Mbps in 2025, up from 223 Mbps in 2024, according to Ofcom's Connected Nations 2025 report published in November 2025. Gigabit-capable broadband now reaches 87% of UK premises, with full fibre (FTTP) overtaking FTTC for the first time in Q3 2025. Median real-world speeds are closer to 80-100 Mbps because millions of homes still run on FTTC copper.
In the US, the FCC's broadband benchmark was raised to 100 Mbps down / 20 Mbps up in March 2024, replacing the previous 25/3 target that had stood since 2015. Ookla's Speedtest Global Index put the US median fixed download speed at roughly 280 Mbps in early 2026, ahead of the UK median but behind Singapore, France, and Chile.
| Country | Median Fixed Download | Median Mobile Download |
|---|---|---|
| Singapore | ~380 Mbps | ~140 Mbps |
| United States | ~280 Mbps | ~180 Mbps |
| United Kingdom | ~170 Mbps | ~95 Mbps |
| Germany | ~135 Mbps | ~85 Mbps |
| India | ~65 Mbps | ~95 Mbps |
Source: Ookla Speedtest Global Index, January 2026 snapshot.
Why Does Real Throughput Fall Short of Advertised Speed?
Marketing speeds describe the link layer, not the application. Several layers of overhead eat into the number before your browser sees the data.
- Protocol overhead. TCP/IP headers, TLS handshakes, and retransmissions consume roughly 5-10% of raw bandwidth on a healthy connection.
- WiFi losses. A 1 Gbps fibre line delivered over 2.4 GHz WiFi from another room often produces 100-300 Mbps at the device. The wire is fast; the air is not.
- Server-side throttling. Many CDNs and file hosts cap per-connection downloads to a few tens of MB/s even if your line is faster.
- Peak-time congestion. UK evening speeds can drop 15-20% below off-peak values on contended cable and FTTC connections.
- Distance to the exchange. FTTC speeds degrade sharply beyond 300-400 metres of copper; a 70 Mbps sync rate can fall to 20 Mbps at 1 km.
Treat advertised speed as a ceiling, not a floor. If your ISP sells "up to 500 Mbps" and a wired speed test gives you 420 Mbps, that is a good result.
Common Mistakes When Comparing Speeds
- Mixing bits and bytes. Calling a 100 Mbps plan "100 MB per second" overstates reality by 8x. The correct figure is 12.5 MB/s.
- Ignoring upload speed. Cable connections often ship at 500/50 Mbps - great for downloads, poor for video calls and cloud backups. Symmetrical fibre (500/500) is a different product even at the same headline number.
- Testing over WiFi. A speed test from a laptop on 2.4 GHz WiFi two rooms away does not tell you what your line can do. Plug in with Ethernet to see the truth.
- Expecting one device to saturate the line. A single HTTP/1.1 download to one server rarely fills a gigabit line; you need parallel streams or a tool like aria2c to actually use the bandwidth you pay for.
- Confusing latency with bandwidth. Gaming and video calls care about round-trip time (ping), not peak throughput. A 50 Mbps connection with 15 ms ping beats a 500 Mbps connection with 120 ms ping for Fortnite.
Where Do These Units Come From?
The bit as a unit of information was formalised by Claude Shannon in his 1948 paper "A Mathematical Theory of Communication", published in the Bell System Technical Journal. A byte was standardised at 8 bits in the IBM System/360 era (1964), though earlier machines used 6, 7, or 9-bit bytes. The SI prefixes kilo, mega, and giga are defined by the International Bureau of Weights and Measures (BIPM) as powers of 10. The binary prefixes kibi, mebi, and gibi were introduced by the IEC in 1998 (IEC 60027-2) specifically to end the 1000-vs-1024 ambiguity in computing, though adoption has been patchy - most operating systems still show "GB" when they mean GiB.
For converting between number bases used in networking, try the Number Base Converter. For binary and decimal conversions, the Binary to Decimal Converter is focused on that use case. If you need to convert physical units instead of data, the Length Converter covers metres, feet, miles, and more. All calculations run in your browser.
Sources
Frequently Asked Questions
What is the difference between Mbps and MBps?
Mbps (megabits per second) is used by ISPs to advertise internet speeds. MBps (megabytes per second) is what your operating system shows for file downloads. There are 8 bits in a byte, so 100 Mbps equals 12.5 MBps.
How accurate is the download time estimate?
The estimates show the theoretical best case based on your chosen speed. Real-world downloads are typically slower due to network overhead, server limits, routing, and congestion. Expect actual times to be 10-30% longer.
What bandwidth units does this tool support?
It supports bps, Kbps, Mbps, Gbps, Tbps for bits per second, and B/s, KB/s, MB/s, GB/s for bytes per second. All conversions use SI (base-10) units as is standard for networking.
Why do ISPs use bits instead of bytes?
Networking has historically used bits because data travels over wires one bit at a time. Using bits also produces larger numbers, which can make connection speeds sound faster in marketing materials.
What internet speed do I need for streaming?
For HD (1080p) streaming, about 5-10 Mbps is sufficient. For 4K streaming, you need 25 Mbps or more per stream. Video calls typically need 3-5 Mbps upload and download.
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