Stopwatch

Precise timing with lap support

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What Is a Stopwatch?

A stopwatch measures elapsed time with high precision. From track events and swimming to laboratory experiments and cooking, stopwatches are essential for any activity where timing matters. Modern digital stopwatches measure to the millisecond (1/1000th of a second) and support lap recording — capturing split times without stopping the count.

This web stopwatch uses your browser's performance timer for millisecond precision. Start and stop freely, record as many laps as you need, and reset to zero when done. Results can be exported for analysis.

How to Use the Stopwatch

  1. Click Start to begin timing.
  2. Click Lap to record a split time without stopping the timer.
  3. Click Stop to pause the timer at any moment.
  4. Click Reset to clear all laps and return to zero.

Timing Formulas & Display Format

Elapsed time = Current time − Start time Lap time = Current time − Previous lap timestamp Total time display: HH:MM:SS.mmm HH = hours MM = minutes (00–59) SS = seconds (00–59) mmm = milliseconds (000–999) Performance.now() precision: ~0.1ms in most browsers

Browser timers use performance.now() which measures wall-clock time. For very long runs (hours), there may be slight drift — for scientific measurements exceeding a few hours, use a dedicated hardware timer.

Practical Examples

100m Sprint

Elite athletes complete the 100m dash in roughly 10.00 seconds. Use the stopwatch to time your own sprints and track improvement over training sessions.

Boiling Eggs

For a perfect soft-boiled egg, time exactly 6 minutes 30 seconds from when the water returns to a boil. The lap feature lets you time multiple eggs at once.

Interval Workout

Structure a 3-set interval: 30 seconds of high-intensity effort, then 30 seconds of rest. Use lap recording to log each work and rest period for post-workout review.

Frequently Asked Questions

How accurate is a browser stopwatch?▾
Most modern browsers provide timer resolution of around 0.1ms using performance.now(). This is more than sufficient for sports, cooking, and general use. For scientific experiments requiring sub-millisecond accuracy, a dedicated hardware timer is recommended.
How do I record lap times?▾
While the stopwatch is running, click the Lap button. The current elapsed time is saved as a split — the main timer keeps running uninterrupted. You can record as many laps as you like.
Can I use it for long durations like hours?▾
Yes. The display shows hours, minutes, seconds, and milliseconds. For typical use cases (workouts, cooking, short experiments), browser timers are accurate over hours. For multi-hour scientific measurements, note that browsers may introduce slight drift.
What is the difference between a timer and a stopwatch?▾
A stopwatch counts up from zero, measuring how much time has passed. A countdown timer starts from a preset value and counts down to zero, triggering an alert when it reaches the end. This tool is a stopwatch — for countdown use, see the Countdown Timer.
How are milliseconds displayed?▾
The display format is MM:SS.mm — minutes, seconds, and two digits representing centiseconds (hundredths of a second). One centisecond equals 10 milliseconds. Internally, timing is tracked to full millisecond precision.