Online Stopwatch

How to use

1. Press Start or the Space bar to begin measuring elapsed time.
2. Press Lap or L whenever you need a split; the stopwatch keeps running.
3. Press Pause to stop and Resume to continue from the same reading.
4. Download CSV to save lap number, split time and total time for a spreadsheet.

Milliseconds are display resolution, not certified race timing

This stopwatch shows three digits after the decimal point: 1 millisecond is 0.001 second, so 1 second contains 1,000 milliseconds. The displayed value is useful for comparing repeated personal attempts, software tasks and classroom experiments. It is not a substitute for a certified sporting timing system: a browser, device scheduling and the person pressing Start or Lap all affect the recorded result. For ordinary training, use the same device and method when comparing laps.

Why the stopwatch survives background tabs and refreshes

The clock stores the actual start timestamp and calculates elapsed time from the current clock instead of adding one tick for every screen update. That means a browser slowing a background tab does not make the elapsed value fall behind when you return. The current start time, paused reading and lap list are kept only in this browser’s local storage, so refreshing the page restores an active or paused session. Reset is the only action that clears that saved session.

Use a CSV lap log in a spreadsheet

Each downloaded CSV has three columns: lap number, lap time and total time. Lap time is the interval since the preceding lap; total time is the elapsed reading from Start. CSV is plain text, so it opens in spreadsheet applications such as Excel, Google Sheets and LibreOffice Calc without an account. The download uses UTF-8 text and includes a byte-order mark, which helps spreadsheet software recognize Korean headers correctly.

Frequently asked questions