Accurate stopwatch with laps, split times, and simple controls.
Ready to start.
Stopwatch
A stopwatch counts upward from zero and records how much time passes. ClockUnit's stopwatch adds lap recording with automatic best/worst highlighting, cumulative split times, and a live average, all running entirely in your browser.
How it works
Tap Start and the clock begins counting up immediately. A pulsing indicator confirms it's running. The display updates in real time to centiseconds.
Press the Lap button at any checkpoint — the end of a sprint, a pool length, a set at the gym. Lap time and cumulative split are recorded instantly.
Hit Stop to pause or finish. Scroll the lap list to see every split with best/worst highlighted. Press Reset when you're ready for a new session.
Features
Every detail designed around accurate timing.
Displays hundredths of a second in real time. All timing uses wall-clock arithmetic so switching tabs never causes drift.
Tap Lap at any moment to record that split. There's no limit — record 2 laps or 200. The list scrolls smoothly.
Fastest lap is highlighted green, slowest in red, and the average is shown in the summary row — instant performance insight.
Each lap shows both its individual time and the cumulative split — the two numbers you actually need for analysis.
Stop the clock during genuine breaks and resume exactly where you left off. Total elapsed time is always accurate.
The Lap button records at the exact millisecond you press it. Timing is always precise.
Settings are saved locally in your browser. Your lap data never leaves your device.
Fully responsive on mobile, tablet, and desktop. No app to install — just open and start.
Use cases
Any activity that needs a start, a stop, and a record.
Record splits for every mile or 400m lap. Best/worst highlights show where you surged and where you faded.
Time each working set and rest period. Know exactly how long your rests are so you can shorten them progressively.
Record each pool length as a lap to track pace consistency across a long swim set or open-water practice.
Start when you sit down, stop when you stand up. Honest time tracking for deep work — no faking it.
Record reference points as you cook — pasta in, sauce added, plate up — without losing your total elapsed time.
Record every sprint attempt as a lap. Compare runs to each other to track speed progression over time.
FAQ
Timing uses Date.now() which is accurate to within a few milliseconds on modern devices. The display updates at ~60fps and shows centiseconds (hundredths of a second). Manual reaction time when pressing Start/Lap adds ±100–200ms.
Lap time is how long that specific lap took from the previous lap (or from start). Split time is the cumulative elapsed time at the moment that lap was recorded. For example: lap 1 = 01:32.45 (lap time), split = 01:32.45; lap 2 = 01:28.11 (lap time), split = 03:00.56.
Yes. The timer uses wall-clock time (Date.now()) internally. Even if the browser throttles the display interval when the tab is hidden, the elapsed time shown when you return is accurate.
Yes. Stop pauses the stopwatch without clearing it. Press Start again and timing resumes from exactly where it left off. Use this for genuine breaks so your total reflects actual activity time.
The lap with the shortest time is highlighted green (best) and the one with the longest time is highlighted red (worst). These highlights only appear when there are two or more laps — a single lap has no comparison basis.
Yes. The Lap button is only visible while the stopwatch is running. Tapping it records the split instantly without stopping or pausing the clock.
No hard limit. The lap list scrolls vertically so you can record as many laps as you need. Very long sessions (hundreds of laps) may use slightly more browser memory, but performance remains smooth.
Open Settings (the gear icon) and disable 'Show centiseconds'. The display switches to MM:SS or HH:MM:SS format instantly.
