Stopwatch
Accurate online stopwatch with millisecond precision, lap tracking, split times, and background tab accuracy.
Privacy First: 100% Client-Side Processing
Processed in your browser. Files are never uploaded.
How to Use the Stopwatch – Online Millisecond Accurate Stopwatch
- 1Click 'Start' (or press the Spacebar) to begin timing.
- 2Click 'Lap' (or press 'L') while running to record split and lap intervals.
- 3Click 'Pause' (or press Spacebar) to halt timing without losing records.
- 4Click 'Reset' (or press 'R') to clear all recorded times and laps.
Formula & How It Works
High-Resolution Performance Timing Method
Unlike traditional setInterval timers that drift during browser thread throttling, our stopwatch tracks elapsed time via window.performance.now() microsecond delta timestamps. This guarantees zero accumulated drift when tabs are backgrounded or minimized.
Worked Examples
100-Meter Sprint Benchmark
Input: Single start to finish sprint
Explanation: Tracks elapsed sprint time down to 1/100th of a second.
Multiple Lap Track Running
Input: 4 laps of 400m track
Explanation: Highlights fastest lap (Lap 4: 01:11.50 in green) and slowest lap (Lap 3 in red).
Productivity Pomodoro Interval
Input: 25-minute study focus block
Explanation: Accurately monitors prolonged study sessions with pause and resume flexibility.
Speedcubing Rubik's Solve
Input: Quick hand solve
Explanation: Keyboard spacebar triggers start and stop instantaneously.
Frequently Asked Questions
Does the stopwatch lose accuracy when I switch browser tabs?▼
No. The timer calculates elapsed time based on performance.now() timestamps rather than tick counters, ensuring zero drift in inactive tabs.
What keyboard shortcuts can I use?▼
Spacebar starts and pauses the timer, 'L' records a new lap, and 'R' resets the stopwatch.
Does the stopwatch make noise or sounds by default?▼
No, the stopwatch operates completely silently without distracting audio chimes.
How does the lap comparison work?▼
When two or more laps are recorded, the fastest lap is highlighted with a green badge and the slowest with a red badge.
Can I copy my recorded lap history?▼
Yes, click 'Copy Result' to copy all lap splits and final times directly to your clipboard.
How accurate is performance.now()?▼
performance.now() offers sub-millisecond precision, providing true professional-grade timing in web browsers.
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