How to use the stopwatch
- Start / Stop — begins timing, and stops it without losing the elapsed total. The button becomes Resume so you can continue the same measurement.
- Lap — records the moment without interrupting the clock. Press it at the end of each repetition.
- Reset — returns to zero and clears the lap list.
Everything is also on the keyboard, which matters when you are timing something and cannot look at the screen: Space to start or stop, L to record a lap, R to reset. The shortcuts are ignored while you are typing in a form field.
Reading the lap list
Each row shows two different numbers, and mixing them up is the most common mistake people make with a stopwatch:
- The lap time (middle column) is the duration of that lap alone — the time since the previous lap was recorded.
- The total time (right column) is the cumulative elapsed time since you started, sometimes called the split time.
So if you run four laps of roughly 90 seconds each, the lap column reads about 1:30 four times over, while the total column climbs 1:30, 3:00, 4:30, 6:00. Coaches generally want the lap column, because that is where pacing shows up. Once you have recorded more than one lap, the fastest is highlighted in green and the slowest in red, so a single glance tells you whether you faded, negative-split, or held an even pace.
Precision, and what it actually means
The display resolves to hundredths of a second and the underlying measurement is driven by the browser's animation frame callback, so the number on screen is genuinely that precise. Your reaction time is not. Human reaction to a visual cue averages around 0.20–0.25 seconds, and pressing the button at the exact moment something happens is at best a well-practised approximation.
This matters when interpreting results. Two hand-timed laps 0.05 seconds apart are, for all practical purposes, identical — the difference is inside your own error margin. Official athletics does not hand-time sprints for exactly this reason; electronic timing triggered by a starting pistol and a finish-line beam exists because human operators cannot be trusted at that resolution. For training, coaching, cooking, science homework or timing a process at work, a hand-operated stopwatch is entirely adequate. For anything where hundredths decide an outcome, it is not.
What people time with it
- Running and swimming — interval sessions, repeats, and comparing splits across a set.
- Gym work — time under tension, rest between sets, circuit rounds, and AMRAP or EMOM workouts.
- Cubing and puzzles — solve times, where the lap list gives you a full session at a glance.
- Music practice — how long you actually spent on a passage, as opposed to how long it felt.
- School science — pendulum swings, reaction rates, ramp experiments.
- Work measurement — how long a task, a call or a process step really takes, before you try to improve it.
- Public speaking — rehearsing a talk against its allotted slot.
Frequently Asked Questions
Can I control it with the keyboard?
Yes: Space starts and stops, L records a lap, and R resets. The shortcuts are disabled while a text field has focus.
Are my laps lost if I reload the page?
Yes. The stopwatch is deliberately session-only and starts fresh on every load, so nothing is stored. Copy anything you need before refreshing.
Does it keep running if I switch tabs?
The elapsed time stays correct — it is measured against the system clock rather than counted frame by frame. The display simply stops repainting while the tab is hidden and catches up when you return.
How many laps can I record?
There is no limit. The newest lap appears at the top of the list.
What is the difference between lap time and split time?
Lap time is the duration of one lap in isolation. Split time — shown here as the total column — is the elapsed time from the start up to that point.
Does it work offline?
Yes, the page is cached after your first visit and runs without a connection.
Related tools
A stopwatch counts up. If you need to count down to zero, use the timer; to be alerted at a specific clock time use the alarm; and for two players alternating turns there is the chess clock. To work out the gap between two times, try the time calculator.