What is a 45 minute timer?
A 45 minute timer is an online countdown that runs for exactly 45 minutes and alerts you when it reaches zero. This one is already set when the page opens: press Start or the space bar and it counts down from 45:00, keeps exact time if you switch tabs or lock your phone, and rings until you stop it.
What 45 minutes is good for
Forty-five minutes is a lesson: many school periods run 40 to 50 minutes (45 in Korean middle schools), and it is a common length for a yoga or fitness class, a tutoring session, a webinar and a long focus block. It is also the focus length of the 45/15 Pomodoro variant, which pairs it with a 15-minute break.
For a class, put the timer on the projector in full-screen mode (F) so everyone sees the same countdown; the ring and the large digits are readable from the back of a room. The alarm sound can be set to Soft or None if a loud beep would be disruptive.
Start it in one click
There is nothing to set: the time is loaded, the Start button has keyboard focus on a computer, and the alarm sound, volume and screen settings are remembered from your last visit. If you need a different length, type it into the hours, minutes and seconds boxes or pick another preset below the timer.
It keeps counting in a background tab
The end time is fixed the moment you press Start, so a slow or sleeping tab cannot make it late: whenever the page is drawn it recomputes the remaining time from the clock. The alarm is pre-scheduled on the browser's audio clock and backed by a system timer and a desktop notification, and if the device was asleep when the time came, the page rings as soon as you return and shows how long ago the 45 minutes ended. On iPhone keep the tab on screen, since Safari pauses hidden pages; Keep screen on, which is on by default on phones, prevents auto-lock while it runs.
Alarm, repeat and phone use
Choose Beep, Bell, Digital, Soft, Cuckoo, Chime, Pipe or None and set the volume; all but the cuckoo are generated in the browser and work offline, and the cuckoo is a short clip of about 65 KB fetched once and then kept by the browser. The alarm repeats until you press Stop alarm, Space or Esc, and gives up after 60 seconds. Android phones vibrate as well; iPhones on iOS 17 or later play it even with the silent switch on.
Need a slightly different time?
The 30 minute timer and the 1 hour timer are the neighbouring presets. For a 50-minute period start this one and press +1 min five times, or type 50 into the minutes box; the 45/15 cycle with breaks is a preset in the Pomodoro timer.
Other time tools
For measuring how long something takes, use the stopwatch, which counts up and records laps. For the days and hours until a date, use the countdown. For alternating focus and break periods, the Pomodoro timer runs the whole cycle, and the interval timer repeats work and rest rounds for training. They all share this timer's clock engine, sounds and settings.