20 Minute Timer
Twenty minutes suits reading time, homework, a workout or a dish in the oven. The countdown starts right away – pause, restart or go full screen with a click or the space bar.
Source: MDN: Web Audio API (alarm sound without an audio file). Updated: .
How it is calculated
How the 20 minute timer works
When the page opens, the 20 minutes countdown starts automatically. The timer stores the end time and recalculates the display from the clock on every frame, so it doesn’t fall behind in a background tab.
Browsers only allow sound after a user interaction. Tap the page or press a key once; the alarm is then scheduled on the browser’s audio clock and plays on time, without loading an audio file.
20 minutes in numbers
| Measure | Value |
|---|---|
| Seconds | 1,200 |
| Milliseconds | 1,200,000 |
| Share of an hour | 0.333 |
| Rounds per hour | 3 |
| Rounds in an 8-hour day | 24 |
Basis: 1 minute = 60 seconds, 1 hour = 60 minutes (BIPM SI Brochure, Table 8).
When will the alarm go off?
- Start at 9:00 a.m. → alarm at 9:20 a.m.
- Start at 2:55 p.m. → alarm at 3:15 p.m.
- Start at 11:45 p.m. → alarm at 12:05 a.m.
While it runs, the exact end time is shown below the display. A pause moves the end by the length of the pause.
What is a 20 minute timer good for?
- Reading: a set reading time for kids or for yourself.
- Homework: one subject, twenty minutes, then a break.
- Fitness: a short interval or strength session with a fixed total time.
- Kitchen: baking times from the recipe – the end time shows below the display.
Other lengths
1 minute timer · 2 minute timer · 5 minute timer · 10 minute timer · 15 minute timer · 30 minute timer · 1 hour timer – or any time you like in the online timer with custom input.
Limits
Many phones pause web pages while the screen is locked; the time is correct again after unlocking, but the alarm may not sound. Closing the tab ends the timer. For important wake-up times, use your phone’s alarm clock.
Frequently asked questions
Does the 20 minute timer start automatically?
Yes. The 20 minutes countdown starts as soon as the page opens. “Pause” or the space bar stops it, “Reset” sets it back to the start.
How many times do 20 minutes fit into an hour?
Three times: 3 × 20 = 60. A 20 minute block is one third of an hour.
Does the 20 minute timer keep running if I switch tabs?
Yes. It works from the end time instead of counting along, so it is correct as soon as you come back. Closing the tab stops it, though.
Why is there no alarm sound?
Browsers only play sound after a user interaction. Tapping the page or pressing a key once is enough. Also check the volume, the mute switch and the “Play sound when time is up” box.
Can I change the time?
Yes. Change hours, minutes and seconds in the form or pick a preset (1 to 60 minutes). The general timer handles any length up to 99 hours.
Sources and legal basis
- MDN: Web Audio API (alarm sound without an audio file)
- MDN: Autoplay guide for media and Web Audio (sound only after user interaction)
- BIPM: SI Brochure, Table 8 (1 min = 60 s, 1 h = 3,600 s)
As of:
Related tools
- Online TimerFree online countdown timer: enter any time or tap a 5, 10 or 15 minute preset, get an alarm when time is up, remaining time in the tab. No sign-up.
- 15 Minute TimerFree 15 minute timer that starts as soon as the page opens, counts down to the second and rings at zero. Full screen and pause, no video ads.
- 30 Minute TimerFree 30 minute timer that starts as soon as the page opens, counts down to the second and rings at zero. Full screen and pause, no video ads.
- Pomodoro TimerPomodoro timer in your browser: 25 min focus, 5 min break, long break after 4 rounds. Free, no sign-up, alarm sound, keeps running in background tabs.
- 1 Hour TimerFree 1 hour timer that starts as soon as the page opens, counts down to the second and rings at zero. Full screen and pause, no video ads.
- 1 Minute TimerFree 1 minute timer that starts as soon as the page opens, counts down to the second and rings at zero. Full screen and pause, no video ads.