Bandwidth and Transfer Calculator
Estimate transfer time, transferable data or required bandwidth. Decimal/binary units, configurable efficiency and exact local arithmetic.
A local estimate, not a network measurement. Entered or required rates are nominal; efficiency determines useful throughput.
Input
Enable JavaScript for local calculation. The guide remains accessible.
Results
Choose a mode and enter its two values.
Round to nearest, half up (0–18 decimal places). Copy preserves the exact value: terminating decimal or fraction n/d. A rounded display can lose precision.
Understanding the estimates
1 B = 8 b. Decimal prefixes use powers of 1,000; binary Ki/Mi/Gi/Ti prefixes use powers of 1,024. Source and result units are chosen explicitly. For rates, Mb/s means Mbit/s and MB/s means megabytes/s.
Theoretical time = data / rate. Theoretical volume = rate × time. Required useful rate = data / time. Efficiency e is the percentage divided by 100: time and required nominal rate are divided by e, transferable volume multiplied by e.
Example: 1 GB at 100 Mbit/s takes 80 theoretical seconds, or 160 seconds at 50%. That rate transfers 1 GB in 80 seconds at 100%. Moving 1 GB in 80 seconds requires 100 Mbit/s useful throughput, or 200 Mbit/s nominal at 50%. These are neither measurements nor network guarantees.
Exact BigInt fractions, no intermediate floating-point arithmetic. Recurring decimals are shown as reduced fractions n/d; only the display is rounded. Input accepts decimals, not n/d fractions. Results may exceed input limits; no exact round trip is promised from rounded values.
A comma is a decimal separator, never grouping; write 0.5 rather than .5. Leading zeros and surrounding spaces count towards limits. A zero rate cannot determine time; zero time cannot determine a rate. Zero volume is still possible.
No sending or storage by this tool. Third-party scripts, extensions and the clipboard can expose values. No file or speed test is transmitted.
Frequently asked questions
What does efficiency mean?
An assumption about useful throughput, from 1 to 100%. It measures neither packet loss nor latency. At 50%, useful volume halves; time or required nominal rate doubles.
Why is a result a fraction?
Some results recur: transferring 8 bits at 3 bits/s takes exactly 8/3 seconds. Copy preserves that fraction, not a decimal approximation.
Are bits, bytes and prefixes distinguished?
Yes: b = bit, B = byte, 1 B = 8 b; MB and MiB represent different volumes. Unit choices also define the result unit.