Watch time at 1.25×, 1.5× and 2× speed

Every playlist result on this site shows watch time at 1.25×, 1.5×, 1.75× and 2×. The maths is trivial — divide by the speed — but the interesting questions are whether the time saved is real, and whether you learn less. Here is what we know.

The time savings

Speed	Share of the original time	A 10-hour playlist becomes
1×	100%	10 h 0 m
1.25×	80%	8 h 0 m
1.5×	67%	6 h 40 m
1.75×	57%	5 h 43 m
2×	50%	5 h 0 m
2.5×	40%	4 h 0 m

Notice the savings flatten. Going from 1× to 1.5× saves 3 h 20 m on a 10-hour playlist; going from 1.5× to 2× saves another 1 h 40 m; 2× to 2.5× saves just one more hour, and (as we'll see) that last step is where comprehension starts to fall. 1.5× is the sweet spot for most people; 2× for material you already half-know.

Common video lengths at each speed

Divide the length by the speed: 1 hour at 1.5× is 60 ÷ 1.5 = 40 minutes.

Video length	1.25×	1.5×	1.75×	2×
30 min	24 m	20 m	17 m 9 s	15 m
45 min	36 m	30 m	25 m 43 s	22 m 30 s
50 min	40 m	33 m 20 s	28 m 34 s	25 m
1 h	48 m	40 m	34 m 17 s	30 m
1 h 20 m	1 h 4 m	53 m 20 s	45 m 43 s	40 m
1 h 30 m	1 h 12 m	1 h	51 m 26 s	45 m
2 h	1 h 36 m	1 h 20 m	1 h 9 m	1 h
3 h	2 h 24 m	2 h	1 h 43 m	1 h 30 m

What the research says

The most direct study is Murphy, Hoover, Agadzhanyan, Kuehn and Castel, "Learning in double time: The effect of lecture video speed on immediate and delayed comprehension" (Applied Cognitive Psychology, 2022). UCLA students watched recorded lectures at 1×, 1.5×, 2× or 2.5× and were tested immediately and again a week later.

The findings, in plain terms:

Up to 2×, comprehension held up. Scores at 1.5× and 2× were not meaningfully different from 1×, on both the immediate test and the delayed one.
2.5× was where it broke. Performance declined beyond 2×.
How you use the saved time matters. Watching once at 2× and then again at 2× shortly before the test beat watching once at 1× a week earlier. In other words, one fast pass plus a fast review close to when you need the material did better than a single slow pass.

Caveats worth keeping in mind before you crank everything to 2×: the lectures were ~15 minutes, in English, to native-speaker undergraduates, and the tests were factual recall. Dense maths, a second language, or anything where you need to do something while watching all argue for slower.

A practical speed guide

Content	Suggested speed	Why
Slow-paced talking-head lectures, familiar topic	1.75–2×	Redundancy is high; the research above applies directly
Standard university lectures, new topic	1.25–1.5×	Keeps room to think; still saves a third of the time
Code-along tutorials	1× (pause often)	You're typing; the bottleneck is you, not the video
Maths and derivations	1–1.25×	Symbol density; you need to follow each step
Non-native language, heavy accent	1× with captions, or 1.25×	Comprehension drops fast when you can't parse speech
Review of something you've already watched	2×	Exactly the case where the study found fast review pays off
Conference talks, podcasts, interviews	1.5–2×	Low information density per minute

Two more habits that matter more than the speed setting:

Spend the saved time on retrieval, not on more videos. The study's best-performing group used the time for a second pass. Notes, flashcards, or the course's exercises work the same way.
Slow down for the parts that matter. Speed is per session, not per course. Watch the summary at 2× and the hard middle section at 1×.

How to change the speed on YouTube

Desktop (youtube.com): click the gear icon → Playback speed → pick a preset, or Custom for 0.05 increments. Keyboard: Shift + . speeds up by 0.25×, Shift + , slows down.

Mobile app: tap the video → the gear (or ⋮) → Playback speed. Long-press anywhere on a playing video for a temporary 2× while you hold.

Limits: standard accounts get 0.25× to 2×. Speeds above 2× (up to 4×, in 0.05 steps) are a YouTube Premium feature. Given the research, that is not a feature most learners are missing.

On this site: the speed chips and slider on a result page recompute the total, the remaining time and the planner instantly, and the speed is remembered in the link you share.

Worked example

A 60-video course, 40 hours total.

At 1×, 1 hour a day, weekdays only: 40 sessions, about 8 weeks.
At 1.5×, same routine: 27 sessions, about 5.5 weeks.
At 1.5× for the lectures, 1× for the 12 code-along videos (say 8 of the 40 hours): 21 h + 8 h = 29 h → 29 sessions, about 6 weeks — and you actually did the exercises.

That last plan is the one most people should make. Set the speed on the result page, tick the code-alongs as you finish them, and the planner keeps the finish date honest.

Summary

Savings flatten after 1.5×; 2× halves the time, 2.5× only shaves a little more.
Comprehension holds up to 2× for lecture-style content in the best available study; it drops at 2.5×.
Use the saved time to review, and slow down for anything you have to do with your hands.