# What is the download time?

Computes how long a file takes to download (or upload) from its size and the connection speed in Mbps, or the speed needed to finish in a given time, or the size that fits in a time.

- Page: https://www.acalculator.org/logic/download-time-calculator
- JSON spec: https://www.acalculator.org/logic/download-time-calculator.json
- Version: 89819a8368f4

## Default answer

Example with the default inputs (File size 5 GB, Speed (Mbps) 100): Downloading 5 GB at 100 Mbps takes 6.667 min (6 minutes, 40 seconds).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| size | File size | The size of the file or data to transfer. |
| mbps | Speed (Mbps) | The connection speed in megabits per second (Mbps), as internet plans and speed tests show it. |
| time | Download time | How long the transfer takes at the full speed. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| size | File size | The size of the file or data to transfer. |
| speed | Speed (Mbps) | The connection speed in megabits per second (Mbps), as internet plans and speed tests show it. |
| time | Download time | How long the transfer takes at the full speed. |
| clock | In hours and minutes | The download time in days, hours, minutes and seconds, rounded half up to the whole second. |
| megabytes | Speed in MB/s | The same speed in megabytes per second (Mbps ÷ 8), as download managers show it. |

## Method

time = size in bytes × 8 ÷ (speed in Mbps × 1,000,000); size = time × speed × 1,000,000 ÷ 8; speed = size × 8 ÷ (time × 1,000,000).

## Assumptions

- The whole connection speed goes to this one file. Real downloads are often slower: protocol overhead, Wi-Fi, a busy server or other devices on the line all take a share.
- Speeds are in megabits per second (Mbps): 1 Mbps is 1,000,000 bits per second, and 1 byte is 8 bits.
- File sizes use SI prefixes (1 GB = 10⁹ bytes) or binary prefixes (1 GiB = 2³⁰ bytes), whichever unit you pick.
- Every step is exact on the numbers as typed; values are rounded only for display.

## Worked examples

1. size = 5,000,000,000, mbps = 100 gives time = 400, clock = 6 minutes, 40 seconds, megabytes = 12.5. Source: SI prefixes giga = 10⁹, mega = 10⁶ (NIST, https://www.nist.gov/pml/owm/metric-si-prefixes).
2. size = 734,003,200, mbps = 8 gives time = 734.0032, clock = 12 minutes, 14 seconds, megabytes = 1. Source: Binary prefix mebi = 2²⁰ (NIST, https://physics.nist.gov/cuu/Units/binary.html).
3. size = 50,000,000,000, time = 3,600 gives mbps = 111.111111, clock = 1 hour. Source: 50 × 10⁹ × 8 ÷ 3,600 ÷ 10⁶ = 111.1 Mbps (SI prefixes, NIST https://www.nist.gov/pml/owm/metric-si-prefixes).
4. mbps = 1,000, time = 60 gives size = 7,500,000,000. Source: 60 s × 1,000 × 10⁶ bits per second ÷ 8 = 7.5 × 10⁹ bytes = 7.5 GB (SI prefixes, NIST https://www.nist.gov/pml/owm/metric-si-prefixes).

## FAQ

### How do I calculate download time?

Turn the file size into bits (1 byte is 8 bits) and divide by the speed in bits per second. A 5 GB file is 5 × 10⁹ × 8 = 4 × 10¹⁰ bits; at 100 Mbps (10⁸ bits per second) it takes 4 × 10¹⁰ ÷ 10⁸ = 400 seconds, or 6 minutes 40 seconds.

### What is the difference between Mbps and MB/s?

Mbps is megabits per second, the unit internet plans and speed tests use. MB/s is megabytes per second, which many download managers show. A byte is 8 bits, so 100 Mbps is 12.5 MB/s.

### Why is my download slower than the calculator says?

The calculator assumes the whole speed goes to one file. In practice some of the line is used by protocol overhead, Wi-Fi loss, other devices and the server at the other end, so real downloads often take longer. Run a speed test and use that number for a closer estimate.

### What speed do I need to download a file in a set time?

Enter the file size and the time, and leave the speed empty. To download 50 GB in one hour you need 50 × 10⁹ × 8 ÷ 3,600 = 111.1 million bits per second, about 111 Mbps.

### Is a GB 1,000 MB or 1,024 MB?

Both are in use. GB (gigabyte) is 10⁹ bytes in SI units, and GiB (gibibyte) is 2³⁰ = 1,073,741,824 bytes. Some operating systems show GiB values with the label GB, so pick GiB in the unit list if your file size comes from one of them.

### Does this work for upload time too?

Yes. The maths is the same: use your upload speed, which on many home plans is much lower than the download speed.

## Sources

- NIST, Metric (SI) prefixes: kilo 10³, mega 10⁶, giga 10⁹, tera 10¹². https://www.nist.gov/pml/owm/metric-si-prefixes
- NIST, Prefixes for binary multiples (IEC 60027-2): kibi 2¹⁰, mebi 2²⁰, gibi 2³⁰. https://physics.nist.gov/cuu/Units/binary.html