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Download Time Calculator

Computes how long a file transfer takes from the file size (MB, GB, TB) and the connection speed (Mbit/s, MB/s or Gbit/s), converting bytes to bits at 8 bits per byte with decimal (SI) prefixes.

When to use

You want to estimate how long a download, upload or backup will take at a given bandwidth, or compare connection speeds.

Do not use when: You need to convert between data-storage units themselves (use data-storage); real transfers are also slowed by protocol overhead, server limits and Wi-Fi conditions.

Formula

bits = file_size × bytes_per_unit × 8 (MB 10⁶, GB 10⁹, TB 10¹² bytes); bits_per_second = speed × (Mbit/s 10⁶, MB/s 8×10⁶, Gbit/s 10⁹); seconds = bits / bits_per_second

Uses decimal prefixes as network operators and drive makers do. Operating systems often report sizes in binary units (1 GiB = 1.074 GB), and real throughput is typically 5–15% below the nominal line speed.

Inputs

Parameter	Type	Required	Description
`file_size`	number	yes	Size of the file in the chosen unit. Range: > 0, ≤ 1000000000
`size_unit`	enum: mb \| gb \| tb	default gb	Unit of file_size (decimal SI prefixes).
`speed`	number	yes	Transfer rate in the chosen unit. Range: > 0, ≤ 1000000000
`speed_unit`	enum: mbit_per_s \| mbyte_per_s \| gbit_per_s	default mbit_per_s	Unit of speed. Internet plans are quoted in megabits per second (Mbps); browsers show megabytes per second (MB/s), which is 8 times larger per unit.

Outputs

Output	Type	Unit	Description
`seconds`	number	s	file_size in bits / speed in bits per second.
`time_formatted`	string		Same time as h:mm:ss.
`minutes`	number	min	seconds / 60.
`hours`	number	h	seconds / 3600.
`speed_mb_per_s`	number	MB/s	Connection speed expressed in megabytes per second.

Example

4.7 GB at 100 Mbit/s: {"file_size":4.7,"size_unit":"gb","speed":100,"speed_unit":"mbit_per_s"} → {"seconds":376,"time_formatted":"0:06:16","minutes":6.27,"hours":0.104,"speed_mb_per_s":12.5}

1 TB at 1 Gbit/s: {"file_size":1,"size_unit":"tb","speed":1,"speed_unit":"gbit_per_s"} → {"seconds":8000,"time_formatted":"2:13:20","minutes":133.33,"hours":2.222,"speed_mb_per_s":125}

GET https://tttkmbb.com/api/v1/calculate/download-time?file_size=4.7&size_unit=gb&speed=100&speed_unit=mbit_per_s

Machine access

API: GET https://tttkmbb.com/api/v1/calculate/download-time (query parameters) or POST with a JSON body {"inputs": {...}}
Schema: https://tttkmbb.com/api/v1/calculators/download-time · Markdown: https://tttkmbb.com/everyday/download-time.md · JSON definition: https://tttkmbb.com/everyday/download-time.json
MCP: server https://tttkmbb.com/mcp, tool run_calculator with calculator_id="download-time"
OpenAPI operationId: estimate_download_time
Freshness: static. Authentication: none. Rate limit: fair use (see rate limits).

Sources

Data-rate units (Wikipedia) (reference)
NIST – Prefixes for binary multiples (standard)

FAQ

Why is my download slower than the calculator says?

The estimate uses the nominal link speed; protocol overhead, the server's upload limit, Wi-Fi signal and other traffic usually cut throughput by 10% or more.

Mbps or MB/s – which one do I have?

Internet plans quote megabits per second (Mbps); download managers show megabytes per second (MB/s). 100 Mbps equals 12.5 MB/s.

Related calculators

Data Storage Converter — Convert between MB, GiB, TB and other data units.
Time Converter — Convert seconds to minutes, hours and days.