Online Stopwatch

How to use the online stopwatch

1. Press Start (or Space). The readout counts up as MM:SS.hh, with the hours shown only once you pass one hour.
2. Press Lap (or L) at each checkpoint. The lap goes into the table with its own time and the running total. The clock itself never stops.
3. Press Stop to pause. The button changes to Resume, and the time carries on from where it stopped.
4. Press Reset (or R twice within two seconds) to clear the time and the laps. The tool holds up to 1,000 laps; after that the Lap button does nothing.
5. Copy CSV, Copy as text or Download CSV to take the laps into a spreadsheet or a note.

Nothing is uploaded. The timing, the lap table and the CSV file are all produced in your browser, and the only thing saved is the current stopwatch state in this browser's local storage so that a reload does not lose it. Reset clears it.

Keyboard shortcuts

The shortcuts are ignored while you type in a text field and when a modifier key such as Ctrl, Alt or Cmd is held, so they do not clash with browser shortcuts. Holding a key down does not repeat the action.

Lap time versus split time

A lap time is the time for one segment: from the previous lap press to this one. A split time (shown here as Total) is the time from the very start to this press. Each split is the sum of all lap times so far, and each lap time is the difference between two splits. The stopwatch stores the splits and works the laps out from them. Because each time is cut to hundredths for display, a lap shown on screen is the difference of the two displayed splits, so the laps always add up to the displayed total and can differ from the exact lap by up to one hundredth of a second. Here is a run with four laps, calculated by the same code the tool uses:

Lap 2 took 00:39.44, which is the split at lap 2 (01:11.85) minus the split at lap 1 (00:32.41). Lap 4 was the fastest and lap 3 the slowest. The last split, 02:30.02, is the whole run. Use laps when you care about consistency between segments (swim lengths, laps of a track, slides in a talk) and splits when you care about where you were at a given moment.

Fastest and slowest laps

Once you have three or more laps, the quickest is labelled fastest and the longest slowest, in text as well as colour. With fewer than three laps the comparison means little, so nothing is marked. If several laps tie exactly in milliseconds, all of them are marked, and if every lap is identical none is. The comparison uses exact milliseconds, so two laps that show the same hundredth can still differ in the hidden millisecond, and only the truly shorter one is marked.

How accurate is an online stopwatch?

The elapsed time is calculated from timestamps, not by counting timer ticks. When you press Start the page reads the browser's high resolution clock (performance.now()), and every redraw shows "now minus start". The result does not depend on how often the screen refreshes or how busy the page is.

• Background tabs. Browsers slow timers in hidden tabs, commonly to about once a second or less. That only affects how often the number is redrawn. When you come back, the next redraw shows the correct time.
• Resolution. Browsers round the high resolution clock on purpose for privacy, typically to a millisecond or finer, which is well below the hundredth shown here. Screens redraw around 60 times a second, so the last digit changes faster than you can read it.
• You are the limit. Pressing a key or button takes a person a couple of tenths of a second to react. For short events the start and stop presses add more error than the clock does, so compare your own timings using the same method each time.
• System clock changes. The measurement uses a clock that is not affected by changing the date or time on your computer while the page is open.
• Reloading. The page saves when you started on the system clock, because the high resolution clock restarts on every page load. After a reload, the time that passed is worked out from that saved start time. If you change the system time while the page is closed, the restored time will be off by that change.
• Sleep. If the computer suspends while the stopwatch runs, the result depends on the browser and operating system. Keep the machine awake for long timings.

Using the CSV export

The CSV has one row per lap with the columns Lap, Lap time, Total time, Lap ms, Total ms and Note. The millisecond columns are plain numbers, so a spreadsheet can average, sort or chart them without parsing a time format. Rows end with CRLF line breaks and any field containing a comma or quote is quoted. To turn the millisecond columns into hours, see the Seconds to Hours Converter.

What people use a stopwatch for

• Workouts. Interval training, rest periods between sets, and lap times on a track or in a pool.
• Presentations and talks. Time a rehearsal and press Lap at each slide or section to see which part overruns.
• Cooking. Track steeping, proofing or resting when there is no fixed target time.
• Studying. Measure how long a practice problem or a reading block takes, then compare sessions.
• Speed solving. Cubers and puzzle fans can time attempts and use laps for each phase of a solve.
• Work and billing. Time a task, then convert the total with the Time to Decimal Converter for invoices, or add up several durations with the Time Duration Calculator.
• Pace. Combine a lap time with the distance in the Speed Distance Time Calculator.

Tips and common mistakes

• Click the page once before using shortcuts if they do not respond, so the page has keyboard focus.
• Use Lap, not Stop, for a segment you want to keep inside the same run. Stop pauses the whole clock.
• Private browsing or blocked site data means the state cannot be saved. The stopwatch still works but a reload starts from zero.