Download Time Calculator

How to estimate

1. Enter a nonnegative size and choose explicit decimal or binary bytes. Optionally load exact File.size metadata from one local file.
2. Enter positive throughput, checking bits versus bytes, then a 1–100 percent usable-throughput assumption.
3. For identical files, enter their count to estimate serial total data at the same sustained rate, not concurrent per-file bandwidth. Calculate, inspect exact details, and copy/download the complete summary. Reset offers Undo.

Worked examples

100 MB at 100 Mbit/s takes 8 seconds ideally; with 80% usable throughput it takes 10 seconds. Three identical 100 MB files take 24 seconds ideally. 1 GiB at 100 Mbit/s takes exactly 85.89934592 seconds, while 1 GB takes 80 seconds. 10 MiB at 5 MiB/s and 10 MB at 5 MB/s both take two seconds, but represent different byte quantities.

Bits, bytes and exact arithmetic

One byte is eight bits. kB/MB/GB/TB use 1000 to the corresponding power; KiB/MiB/GiB/TiB use 1024. kbit/s, Mbit/s and Gbit/s always use 1000, not 1024. Canonical data is in bits. TotalBits = sizeBits × fileCount; effectiveRate = enteredRate × usablePercent/100; idealSeconds = totalBits/enteredRate; adjustedSeconds = totalBits/effectiveRate.

Decimal parsing, conversions and duration division use reduced BigInt fractions. Displayed whole-second durations round half-up and carry days/hours/minutes correctly. Positive times below one second say “less than 1 second” with detailed seconds and an exact fraction; zero data has exactly zero duration. Exports include exact fractions rather than losing precision. Changing units converts the underlying quantity, never reinterprets it. Converted input displays use up to six decimals; their exact quantities remain stored until a field edit replaces them.

Input rules and limitations

Size: 18 integer digits and six decimals; rate: 12 integer digits and six decimals; percentage: four decimals between 1 and 100. One dot or comma is a decimal separator, not grouping. No exponents, negatives, unit suffixes or internal spaces. Derived durations cannot exceed 10,000 years; 365 days/year is used only to validate that cap, not to make a realistic forecast. Identical-file count is 1–10,000. Invalid/incomplete edits remain editable; prior estimates are marked outdated and exports are disabled until recalculated.

The percentage is an entered sustained payload-rate assumption, not a universal overhead estimate. Setup latency, changing throughput, server limits, contention, retries, compression and storage bottlenecks are excluded. This calculator cannot predict all those effects or reduce actual file size. Local inspection reads File.size only, never file contents; names may appear locally but are omitted from summaries. No network probes, IP collection or external speed-test scripts are used by this tool.