# How long at this playback speed?

Works out how long a video, podcast or lecture takes at a playback speed such as 1.5× or 2×, and the time saved, or the speed you need to finish it in the time you have.

- Page: https://www.acalculator.org/everyday-life/playback-speed-calculator
- JSON spec: https://www.acalculator.org/everyday-life/playback-speed-calculator.json
- Version: 892bb29dc280

## Default answer

Example with the default inputs (Find Time at a speed, Hours 1, Minutes 30, Seconds 0, Playback speed 1.5): At this speed it takes 1 hour.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| find | Find | The new time at a speed, or the speed that fits the time you have. |
| h | Hours | The hours part of the length at normal speed. |
| m | Minutes | The minutes part of the length at normal speed. |
| s | Seconds | The seconds part of the length at normal speed. |
| speed | Playback speed | How many times normal speed you play at, such as 1.5 for 1.5×. |
| th | Hours | The hours part of the time you have. |
| tm | Minutes | The minutes part of the time you have. |
| ts | Seconds | The seconds part of the time you have. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| newTime | Time at this speed | The length at normal speed ÷ the playback speed, to the nearest second. |
| needed | Speed you need | The length at normal speed ÷ the time you have. |
| saved | Time saved | The length at normal speed minus the time at this speed, when faster than 1×. |
| added | Time added | The time at this speed minus the length at normal speed, when slower than 1×. |
| share | Share of the original time | The time at this speed ÷ the length at normal speed, which is 1 ÷ speed. |
| length | Length at 1× | The length at normal speed. |

## Method

time at speed = length ÷ speed, rounded half up to the second; speed needed = length ÷ time you have.

## Assumptions

- The whole recording plays at one speed, with no skipped parts or pauses.
- Times are shown to the nearest second, a half second rounded up; the time saved is the difference of the shown times.
- Players offer set speeds (often 0.25× to 2×, some up to 3× or more); round the speed you need up to one your player has.

## Worked examples

1. find = time, h = 1, m = 30, s = 0, speed = 1.5 gives newTime = {"hours":1,"minutes":0,"seconds":0}, saved = {"hours":0,"minutes":30,"seconds":0}. Source: 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 5,400 s ÷ 1.5 = 3,600 s.
2. find = time, h = 0, m = 45, s = 10, speed = 1.25 gives newTime = {"hours":0,"minutes":36,"seconds":8}, saved = {"hours":0,"minutes":9,"seconds":2}, share = 80%. Source: 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 2,710 s ÷ 1.25 = 2,168 s.
3. find = speed, h = 2, m = 0, s = 0, th = 1, tm = 20, ts = 0 gives needed = 1.5, newTime = {"hours":1,"minutes":20,"seconds":0}. Source: 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 7,200 s ÷ 4,800 s = 1.5×.
4. find = time, h = 0, m = 0, s = 7, speed = 2 gives newTime = {"hours":0,"minutes":0,"seconds":4}, saved = {"hours":0,"minutes":0,"seconds":3}. Source: 1 h = 3,600 s and 1 min = 60 s (NIST Special Publication 811, Appendix B.8, https://www.nist.gov/pml/special-publication-811, retrieved 2026-10-02): 7 ÷ 2 = 3.5 s, shown as 4 s.

## FAQ

### How long is a video at 1.5× speed?

Divide the length by the speed. A 90 minute lecture at 1.5× takes 90 ÷ 1.5 = 60 minutes, so you save 30 minutes. At 2× it takes 45 minutes, half the time.

### How much time does 1.25× save?

At 1.25× a recording takes 1 ÷ 1.25 = 80% of its length, so you save 20%. A 45 minute 10 second podcast takes 36 minutes 8 seconds, 9 minutes 2 seconds less.

### What speed do I need to finish in time?

Divide the length by the time you have. To watch a 2 hour course in 1 hour 20 minutes, you need 120 ÷ 80 = 1.5×. If your player has only set speeds, pick the next one up.

### Does a slower speed add time?

Yes. Below 1× the recording takes longer: 30 minutes at 0.75× takes 40 minutes, 10 minutes more. The calculator shows the time added instead of the time saved.

### How are the seconds rounded?

The new time is the exact length divided by the exact speed, rounded to the nearest second, with a half second rounded up. A 7 second clip at 2× is 3.5 seconds, shown as 4 seconds.

## Sources

- NIST Special Publication 811, Guide for the Use of the International System of Units, Appendix B.8 (1 min = 60 s, 1 h = 3,600 s). https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-02)