Overhead (typically 3–10%) accounts for transfer-protocol service data — TCP/TLS headers, acknowledgments, possible packet retransmissions — which makes real time slightly longer than the theoretical minimum.
Result
This page has no server side at all. The table you paste is parsed by JavaScript inside your own browser, the chart is drawn on a canvas element on your machine, and the export file is assembled locally. Nothing is uploaded, stored or written to any log. You can disconnect from the network after the page has loaded and everything will still work — which is the simplest way to verify the claim yourself.
Facts and limits of this method
| File size | Binary system (1 KB = 1024 bytes), as shown by the operating system |
|---|---|
| Connection speed | Decimal system (1 Kbps = 1000 bit/s), as stated by ISPs |
| Formula | time = (size × file count × (1 + overhead/100)) / speed |
| Upstream speed | For most home connections, noticeably lower than download speed (asymmetric connection) |
When it misleads you
- The upstream (upload) speed of most home internet connections (especially cable and some DSL) is significantly lower than the downstream (download) speed — don't confuse the two when calculating upload time.
- The calculation uses binary units for file size (1 KB = 1024 bytes, as shown by a file manager) and decimal units for connection speed (1 Mbps = 1,000,000 bit/s, as stated by ISPs) — this is a deliberate and typical combination for network calculations, not a mistake.
- Protocol overhead is a simplified allowance for service traffic; the real effective transfer rate depends on many factors (network latency, packet loss, number of simultaneous connections) that this calculation doesn't model in detail.
- The calculation assumes a constant connection speed throughout the transfer, without accounting for real-world fluctuations in network throughput.
How it is calculated
The size of one file is converted to bytes according to the selected unit (powers of 1024).
The total data volume is computed as the size of one file multiplied by the file count and by the factor (1 + overhead / 100).
The connection speed is converted to bytes per second according to the selected unit (powers of 1000, accounting for the difference between bits and bytes).
The total upload time is computed by dividing the total data volume by the speed in bytes per second, and formatted as days, hours, minutes and seconds.
Questions and answers
Why do file size and connection speed use different numbering systems (1024 and 1000)?
This is standard practice in network calculations: operating systems traditionally show file sizes in binary units (1 KB = 1024 B), while ISPs state connection speed in decimal units (1 Mbps = 1,000,000 bit/s) — these are two separate conventions that developed independently.
Why is an upload often slower than the advertised speed would suggest?
Real-world speed is almost always lower than the ISP-advertised figure due to protocol overhead, connection sharing across devices, and other network factors — the "overhead" parameter partly accounts for this.
Why enter a file count instead of just increasing the total size?
If there are many files, you could calculate the combined size as one number — but entering them separately is more convenient when you know the size of one typical file (like a photo) and how many are in the batch.
Is my data sent anywhere?
No, the whole calculation runs in your browser.