How the playback speed formula works
Watch time is the length divided by the speed. A 60-minute lecture at 1.5× takes 60 ÷ 1.5 = 40 minutes, saving 20. At 2× it takes 30 minutes. To find the speed you need, divide the length by the time you have: 90 minutes of video in 60 minutes needs 1.5×.
Quick reference
| Length | 1.25× | 1.5× | 1.75× | 2× |
|---|---|---|---|---|
| 10 minutes | 8m | 6m 40s | 5m 43s | 5m |
| 30 minutes | 24m | 20m | 17m 09s | 15m |
| 1 hour | 48m | 40m | 34m 17s | 30m |
| 1 hour 30 minutes | 1h 12m | 1h 00m | 51m 26s | 45m |
| 2 hours | 1h 36m | 1h 20m | 1h 09m | 1h 00m |
Which speed is comfortable?
- 1.25×: barely noticeable for most speakers; a good default for talks and podcasts.
- 1.5×: comfortable once you’re used to it; saves a third of the time.
- 1.75–2×: works for slow speakers, revision and content you know; harder for dense or technical material.
- Above 2×: mostly useful for skimming to find a section.
Most video players, including YouTube, course platforms, and the video players built into phones and browsers, offer speeds in steps of 0.25×, so a target like 1.6× may round to 1.5× or 1.75×.
Study tips
For lectures, many students watch at 1.5× and slow down for difficult parts rather than rewatching at normal speed. Plan the total: a 12-lecture course of one hour each is 12 hours at normal speed, or 8 hours at 1.5×. If you only need the audio, such as a recorded talk to listen to on the go, save it as an MP3 with Video to MP3, which is much smaller.
Reading the length from a file
Choose a video or audio file and the calculator reads its length on your device, without uploading it, then fills in the result. It works with MP4, MOV, WebM, MP3, M4A and other files your browser can play.
Questions
How long is a 1-hour video at 1.5x speed?
40 minutes, saving 20 minutes.
How long is a 1-hour video at 2x speed?
30 minutes.
How do I work out watch time at a faster speed?
Divide the video length by the speed. For example, 45 minutes ÷ 1.25 = 36 minutes.
What speed do I need to finish a 2-hour video in 1 hour 20 minutes?
1.5×. Divide the length by the time you have: 120 ÷ 80 = 1.5.
Is my file uploaded?
No. Only its length is read, on your device.
CalculatorHow big will your video be? Try the file size calculator