Online timer
Pick a length and press Start: the timer rings at the end. 5 minutes = 300 seconds.
- Checked on thousands of cases
- Updated November 6, 2026
Quick challenge
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Test yourself: every answer is computed by the tool, and the wrong choices are the most common traps.
How it works
Formula: Time left = end time − now
When you start, the tool notes the end time (now + length), then shows the gap with your device's clock at every moment. So the time stays right even when the browser slows the page down. The alarm is made by the browser, with no sound file, and the screen stays on during the countdown when the device allows it.
Worked examples
5 minutes
300 seconds.
25 minutes
The timer shows 25:00 at the start.
90 minutes
1:30:00: an hour and a half.
Common mistakes
Counting 100 seconds to the minute: 3 minutes = 300 s.
A minute is 60 seconds: 3 minutes = 180 s.
Reading 1.5 minutes as 1:50.
0.5 minute = 30 seconds: 1.5 minutes = 1:30.
Locking your phone and counting on the alarm.
Keep the page on screen: many phones pause hidden pages.
What the calculation leaves out
- The time shown stays right in the background, but the browser may delay or mute the alarm when the page is hidden or the phone is locked.
- Your device's volume and silent mode apply to the alarm.
Minutes in seconds and hours
| Minutes | Seconds | h:mm:ss |
|---|---|---|
| 1 min | 60 s | 1:00 |
| 2 min | 120 s | 2:00 |
| 3 min | 180 s | 3:00 |
| 5 min | 300 s | 5:00 |
| 10 min | 600 s | 10:00 |
| 15 min | 900 s | 15:00 |
| 20 min | 1,200 s | 20:00 |
| 25 min | 1,500 s | 25:00 |
| 30 min | 1,800 s | 30:00 |
| 45 min | 2,700 s | 45:00 |
| 60 min | 3,600 s | 1:00:00 |
| 90 min | 5,400 s | 1:30:00 |
Frequently asked questions
Does the timer ring with the screen locked?
Not always: many phones pause web pages when the screen is locked. Keep the page on screen; the tool asks the device to keep the screen on.
Can I add time while it runs?
Yes: the +1 button adds a minute, even after the alarm.
What is the longest timer?
Up to 24 hours (1,440 minutes).