30 Second Timer
A ready-to-go 00:30 countdown -- press Start, or set a different duration below if you need one.
Keyboard: Space start/pause, R reset, Esc stop alarm.
What a 30 second timer is used for
- the standard 30-second television commercial slot
- a quick microwave reheat increment for food that's just slightly cold
- a common rest interval between HIIT work rounds
- a plank-hold progression step for building endurance
- a short pause to let a photo or file finish uploading
Why 30 seconds
Thirty seconds is the traditional base unit of television advertising -- the standard 30-second spot that every other commercial length (15 seconds, 60 seconds) is described relative to -- and it's also a common, well-tested work or rest interval in HIIT-style training, short enough to sustain real intensity through.
30 seconds = 0.5 minutes = 1/120 hour
How it stays accurate
Like every timer on this site, this one never counts down by subtracting one second at a time -- it records the exact target end timestamp the moment you press Start, then recomputes the time left from that fixed target on every screen update. Switching tabs, minimizing the window, or letting the browser throttle a background tab doesn't cost any accuracy, because the next update still does the subtraction fresh rather than trying to catch up on missed ticks. The alarm itself is synthesized with the Web Audio API -- no audio file, nothing an ad blocker could interfere with -- and repeats until you stop it with the Escape key, the Stop alarm button, or by starting a new countdown.
Frequently Asked Questions
What is a 30 second timer good for?
A few common uses: the standard 30-second television commercial slot; a quick microwave reheat increment for food that's just slightly cold; a common rest interval between HIIT work rounds.
How long is 30 seconds in other units?
30 seconds = 0.5 minutes = 1/120 hour.
Does this 30 second timer stay accurate if I switch tabs?
Yes -- it stores the exact moment the countdown should end and recomputes the time left from that fixed target on every update, rather than counting ticks, so a background tab that gets throttled for a while doesn't cost any accuracy.
Why is 30 seconds a notable duration?
Thirty seconds is the traditional base unit of television advertising -- the standard 30-second spot that every other commercial length (15 seconds, 60 seconds) is described relative to -- and it's also a common, well-tested work or rest interval in HIIT-style training, short enough to sustain real intensity through.