Bandwidth Calculator
Transfer times and data volumes for a link speed. Free, and runs entirely in your browser — nothing you enter is uploaded, stored or sent to a server.
About Bandwidth Calculator
How long will this transfer take, at this link speed? The calculation is straightforward but the units are a trap: link speeds are quoted in bits per second, file sizes in bytes. A 100 Mbps connection moves at most about 12.5 MB per second, before any overhead.
Both sides carry their own unit selector, so a 500 MB file over a 100 Mbps line is answered directly, without converting anything by hand first.
Where it helps
- Handles the bits-to-bytes conversion that causes most bad estimates.
- Independent units on the size and speed sides.
- Useful in both directions: a transfer window, or the throughput a deadline demands.
- Covers everything from a small asset to a multi-terabyte migration.
Limits
- The result is a theoretical best case; protocol overhead alone costs several percent.
- Real transfers are limited by latency, congestion, disk speed and the far end, often more than by link speed.
- Advertised speeds are maxima, not guarantees, and are usually asymmetric on consumer connections.
- A single TCP stream rarely saturates a high-latency link, however fast it is.
Frequently asked questions
Why is my 100 Mbps connection only giving me 11 MB/s?
That is close to the theoretical maximum. Divide bits by eight, then subtract protocol overhead — you are getting essentially the full link.
What actually slows a large transfer?
Latency and window size on long paths, disk throughput at both ends, and any per-connection limit. Several parallel streams often beat one.
Should I plan with the advertised speed?
No. Assume 70 to 80% of it for sustained transfers, and measure before committing to a maintenance window.
Is uploading slower than downloading?
On most consumer connections, considerably. Check the upstream figure when the transfer is outbound.
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