21-Second Timer

Set a 21-second countdown in one click. This short timer can mark an interval, hand-washing check, quick brew or another repeatable window.

00:00

Tip: press Space to start or pause, R to reset, F for full screen.

In short

The 21-second timer is a free, full-screen countdown with an alarm, pause and loop. It is preset to 21 seconds (0:21) and ready in one click - Popular for reaction drills, photo & video and more.

Is a 21-Second Timer the Right Length?

Best for: intervals, holds and precise physical cues.

Choose another length for: open-ended work or anything that needs preparation.

Choose the 21-second timer when the finish matters more than checking progress continuously. Pick a shorter timer for urgency, or a longer one when stopping mid-task would be disruptive.

A Sample 21 Seconds Plan

StageTimeWhat to do
Prepare4 secondsChoose one outcome and remove distractions.
Main block13 secondsDo the task without checking another clock.
Finish4 secondsWrap up, save your place and decide the next step.

How to Set a Timer for 21 Seconds

Starting this countdown takes one click. The clock is already set to 0:21. Here is the full flow, including pausing, looping and full screen.

  1. Open the timerYou're already here. This page is preset to 21 seconds, so the countdown loads ready to go with 21 seconds on the clock.
  2. Press StartHit the big Start button (or the Space bar) to begin. The display fills the screen so you can read it from across the room.
  3. Keep workingSwitch tabs or minimise the window. The timer keeps counting in the background and remembers its place if you reload.
  4. Pause, loop or resetPause to grab a break and resume where you left off, switch on Loop to repeat automatically, or reset to run the 21-second countdown again.
  5. Get the alarmAt zero the screen flashes and the page attempts to play the selected sound. Keep the tab open and test audio before relying on it.

Duration and Clock Conversion

This duration spans 21 seconds in total.

That's under a minute - A short, precise countdown.

However you measure it, the 21-second countdown tracks the same span and reaches zero at the scheduled finish time. Alarm sound requires the page to remain open and the browser to permit audio.

Seconds21
Minutes0.35
Hours0.0058
Clock (h:mm:ss)0:00:21

Why This Length Can Work

21 seconds gives you a real challenge without the grind. It is the classic length for a wall sit, a burst of jumping jacks, or letting a face wash do its work. Grab a quick 30-second timer and push through.

Tip: Pick a target before you start 21 seconds, like a set number of squats. A goal turns a short burst into a mini challenge you want to beat.

Tasks That Fit the Available Time

A 21-second window can hold a focused, clearly bounded action. For the strategy behind it, our guide on interval training timer guide for hiit workouts goes deeper. Possible uses include:

  • rest between heavy sets
  • run a sprint interval
  • let a face mask set
  • scrub your hands properly

Use Cases for This Duration

This countdown is useful when its length matches the job. Consider these examples:

Reaction drills

Run a countdown for reflex, speed and agility drills.

Photo & video

Give everyone a heads-up before a group photo or a clip.

Cooling & setting

Let something cool, set or rest for a precise moment.

Interval training

Drive work-and-rest intervals for Tabata, HIIT and circuit sessions.

Plank & wall-sit

Hold an isometric exercise to the exact second and beat your best.

Breathing resets

Take a short, timed breathing break before a call, serve or set.

Using this for training?

Interval Training Timer Guide for HIIT Workouts

Set up interval timers for HIIT, Tabata, EMOM and circuits. Learn the work/rest formats and how to loop a timer so your rounds run hands-free.

Read the guide →

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Questions About This Duration

Can a browser delay the countdown display?
Rather than counting ticks, the timer saves a finish time from your device clock and watches for it. Even if your browser throttles a background tab, the remaining time corrects itself the moment you look back. Keep the tab open and test sound because devices can suppress background audio.
Can I quickly repeat it for intervals?
Turn on Loop and the timer restarts automatically when it ends - Ideal for interval training, circuits and repeated rounds. You can also just press reset to run it again.
How is a short countdown calculated?
The timer saves a finish timestamp from your device clock and recalculates what remains on each update instead of assuming one callback per second.
Can I change or mute the alarm sound?
Yes. Use the sound toggle to mute the alarm at any time. The alert is generated in your browser, so nothing is downloaded. An already loaded page can continue without a connection, subject to browser audio restrictions.
Is there an app to download or an account to make?
Neither. Everything runs on this page in your browser, so there is nothing to install and no sign-up. Open it on any phone, tablet or computer and it behaves the same way.
Is my timer private?
Completely. The timer runs on your device and your settings are stored only in your own browser. Nothing about your countdowns is sent to a server or shared.

Need this countdown on another page? Create an embeddable timer with your preferred title, theme and size.