Bandwidth Calculator
How long will that transfer take? Convert file sizes and connection speeds into real download times (with protocol overhead accounted for), or work backwards from a deadline to the bandwidth you need. Clears up Mbps vs MB/s once and for all. Free, instant, no signup.
Transfer time at 90.0 Mbps effective
14m 49s
Same transfer on common connections
| Connection | Time |
|---|---|
| DSL 10 Mbps | 2h 28m 9s |
| 4G 50 Mbps | 29m 38s |
| Cable 100 Mbps | 14m 49s |
| Fiber 300 Mbps | 4m 56s |
| Fiber 1 Gbps | 1m 29s |
| 10 GbE 10 Gbps | 9s |
Bits, bytes and where the eights go
Connection speeds are sold in bits per second (Mbps, Gbps); file sizes are stored in bytes (MB, GB) — and one byte is eight bits. So a 100 Mbps line moves at most 12.5 MB of data per second, before any protocol overhead. The calculator handles the conversion and lets you model overhead explicitly, so the answer matches what your download actually does.
Checking why a link feels slow? Start with ping for latency and packet loss, and traceroute to find where the path degrades.
Frequently asked questions
What's the difference between Mbps and MB/s?
Mbps is megaBITS per second; MB/s is megaBYTES per second — and a byte is 8 bits. ISPs advertise in bits (100 Mbps sounds better), download managers report in bytes (12.5 MB/s is the same speed). To convert, divide Mbps by 8. Most "my internet is slower than advertised" confusion is exactly this factor of eight.
How long does it take to transfer 1 TB?
At the raw line rate: about 22 hours on 100 Mbps, 2.2 hours on 1 Gbps, and 13 minutes on 10 Gbps. Add protocol overhead and real-world conditions and you're typically 5–15% slower. This is also why for multi-terabyte migrations, shipping physical drives (AWS Snowball et al.) still beats the network — as the saying goes, never underestimate the bandwidth of a station wagon full of tapes.
Why is my actual download slower than my connection speed?
Several layers eat into the headline number: TCP/IP and Ethernet framing overhead (3–10%), TLS encryption, distance-related latency limiting TCP throughput, Wi-Fi loss, the remote server's own upload capacity, and other devices sharing your link. A single HTTP download on a healthy wired 100 Mbps line realistically sustains 85–95 Mbps — the calculator's overhead setting models this.
What is the difference between bandwidth, throughput and latency?
Bandwidth is the theoretical capacity of the link (lanes on the highway); throughput is what you actually achieve (cars that got through); latency is the round-trip travel time for a single packet (how fast one car arrives). A satellite link can have high bandwidth and terrible latency; a short LAN cable has modest bandwidth and sub-millisecond latency. Interactive apps care about latency, bulk transfers about throughput.
How much bandwidth does video streaming use?
Roughly: 3 GB/hour for 1080p (≈7 Mbps), 7–15 GB/hour for 4K (≈16–34 Mbps), 0.7 GB/hour for 720p. A month of 2 hours daily 4K viewing is around 500–900 GB — worth knowing against ISP data caps. Video calls are lighter: 1–2.5 GB/hour depending on quality.
Why do file sizes use GB and GiB inconsistently?
GB (gigabyte) is decimal: 10^9 bytes. GiB (gibibyte) is binary: 2^30 = 1,073,741,824 bytes — about 7.4% bigger. Drive manufacturers use decimal GB, Windows historically displays binary units while calling them GB, and Linux tools mix both. This calculator supports both so your numbers match whichever tool you're reading.
How do I test my actual connection speed?
Run a speed test to a nearby server (wired, not Wi-Fi, for meaningful numbers), then compare against the calculator's estimate for your transfer. For servers, measure with tools like iperf3 between your own endpoints — public speed tests measure the path to the test server, not to your infrastructure.
Slow transfers are a symptom — see them before users do
WatchFor measures response times and transfer performance of your sites and APIs from multiple regions around the clock, so a degrading link shows up as a trend line, not a support ticket.
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