PRACTICAL GUIDES · Units and conversions
Mbps vs MB/s: understanding download time
Distinguish bits, bytes, decimal and binary units and advertised speed. Compare an estimated transfer time with a real download.
By Puffinmint · Updated
Identify bits, bytes and prefixes
A 100 Mbps connection and a 100 MB download use different units: lowercase b means bits and uppercase B means bytes. Identify both the file-size unit and the speed unit before estimating time.
Estimate a transfer with explicit efficiency
Convert the size to bits and divide by the bits transferred each second. Set an efficiency percentage for a more realistic scenario. MB and GB use decimal prefixes; MiB and GiB use powers of 1024 and are not interchangeable labels.
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Input
1 GB; 100 Mbps; 80%
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Calculation steps
Choose and apply the method
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Result
100 s
TRY THIS STEP
Download time calculator
Work inside this guide: load an example, run the tool and edit the inputs to compare results. The second experiment tests a different case.
A reproducible example
A 1 GB file contains eight billion bits. At 100 Mbps its ideal transfer takes 80 seconds. With 80% efficiency the usable rate is 80 Mbps and the estimated duration increases to 100 seconds.
Replace GB with GiB
At 100 Mbps and 80% efficiency, 1 GB takes 100 seconds and 1 GiB takes about 107.3741824. Change only the file unit and compare seconds.
Result
Enter your values to see the result.
One gigabyte at 100 Mbps and 80% efficiency
A 1 GB file contains eight billion bits. At 100 Mbps its ideal transfer takes 80 seconds. With 80% efficiency the usable rate is 80 Mbps and the estimated duration increases to 100 seconds.
Usage scenario
- Input
- 1 GB; 100 Mbps; 80%
- Result
Calculation steps
Convert bytes to bits
Apply efficiency to the speed
Divide the size by the effective speed
Compare the estimate with a real transfer
Measure a sufficiently long transfer and compare like-for-like units. Wi-Fi, competing traffic, the server, storage and protocols can limit throughput. This tool does not measure your network or guarantee a constant advertised rate.
These are example inputs, rather than measurements of a real case. Results use the full tool’s calculation engine. Compare them with the worked steps in this guide, then tick the checks after reviewing.
| Parameter | Value |
|---|---|
| What are the limits of this tool? | File size up to one trillion units; efficiency 1–100%. Assumes constant speed and does not test the network. |
| Processing and privacy | Inputs and results are processed in your browser and are not sent to the server. Aggregate statistics, when enabled, record only the tool and outcome, without the content. |