Online Stopwatch with Laps
A free online stopwatch with lap times. Start, pause, and reset with one click or the keyboard, record unlimited laps, and export the results as text or CSV — timing survives page reloads.
Run the Stopwatch and Record Lap Times
Stopwatch Formula
Where:
- \(t_{\text{elapsed}}\) — total time shown on the stopwatch since the last reset
- \(t_{\text{start}}\) — timestamp of the moment Start (or Resume) was pressed
- \(t_{\text{end}}\) — timestamp of the moment the measurement is read or paused
- \(T_i\) — total elapsed time at which lap number \(i\) was recorded
- \(t_{\text{lap},i}\) — duration of lap \(i\) alone, i.e. the time between two consecutive lap presses
The stopwatch stores timestamps instead of counting ticks, so the elapsed time stays accurate even if you switch tabs, minimize the window, or reload the page. Each lap time is simply the difference between the current total and the total at the previous lap.
Stopwatch – Calculation Example
Example: you start the stopwatch, press Lap after swimming the first pool length, and press Lap again after the second length. The watch shows a total of 00:01:02.45 (62.45 s) at the first press and 00:02:07.65 (127.65 s) at the second.
\[ t_{\text{lap},1} = 62.45 - 0 = 62.45\ \text{s} \]
\[ t_{\text{lap},2} = 127.65 - 62.45 = 65.20\ \text{s} \]
Result: the lap table lists lap 1 as 00:01:02.45 and lap 2 as 01:05.20... lap time 00:01:05.20, both with their totals 00:01:02.45 and 00:02:07.65 (127.65 s). Lap 1 is marked fastest, lap 2 slowest, and the average lap is about 63.8 s.
How to use the calculator
- Press Start (or the Space key) to begin timing; the display shows the elapsed time in
hh:mm:ss.ccformat — hours, minutes, seconds and hundredths. - Press Lap (or the L key) whenever you complete a segment — a lap, a lap, a round, a repetition. Each press adds a row to the Lap Times table with the lap time and the cumulative total.
- Press Pause to freeze the clock (the button then becomes Resume), or Reset (the R key) to zero everything and clear all laps.
- Switch on Keep counting across page reloads to store the stopwatch state in your browser. If the clock is running when you leave or reload the page, it resumes exactly where it should — a running clock keeps counting while you are away. Uncheck the box to erase the saved state.
- Use Copy laps as text or Download CSV to export the lap list for a spreadsheet or notes. Full screen enlarges the display, handy for projecting the clock during a workout or event.
What a stopwatch with laps does
A stopwatch measures elapsed time from a single starting point. What turns it into a training and analysis tool is the lap function: instead of one total at the end, you get a split of every segment along the way. Runners use laps for interval repeats, swimmers for pool lengths, and coaches for recording each athlete in rotation, all while the clock keeps running without interruption.
Each lap entry shows two numbers. The lap time is the duration of that segment alone — how long it took from the previous lap press to this one. The total time is where the cumulative clock stood when the lap was taken. Both matter: totals track overall progress, while lap times reveal consistency, fatigue, or pacing changes from one segment to the next.
The table automatically highlights the fastest and slowest lap (once there are at least two laps with different times) and shows a summary line with the count, fastest, slowest and average lap. A steady spread means even pacing; a lap time drifting upward lap after lap is a classic sign of fatigue. If you need to combine the results with other times, the Time Duration Calculator can subtract splits from one another, and the Time Calculator can add up a session of several runs.
Limits and practical tips
- Accuracy: the display shows hundredths of a second, and times are derived from high-resolution timestamps. Still, this is a browser stopwatch — use a certified timing device for official competitions or record attempts.
- Background tabs: browsers pause visual updates in hidden tabs, but because elapsed time is computed from timestamps, the total (and any lap you press) remains correct when you come back.
- Saved state: with the Keep counting across page reloads box checked, the state is stored in your browser's local storage. In private or incognito mode storage may be blocked — the stopwatch still works, it just resets on reload. Unchecking the box immediately erases the stored data.
- Keyboard shortcuts: Space starts/pauses, L records a lap, R resets. They are ignored while you are typing in a form field, so they will not interfere with other tools on the page.
- Export: the CSV file opens in Excel, Google Sheets and similar tools; the copied text is tab-separated and pastes directly into spreadsheet columns. If your browser blocks clipboard access, use the CSV download instead.
If you end up with lap totals you want to convert to decimal hours for billing or logging, the Hours to Decimal converter turns hh:mm:ss values into decimal format in one step.
Keyboard shortcuts and buttons
| Action | Button | Shortcut |
|---|---|---|
| Start / pause / resume | Start, Pause, Resume | Space |
| Record a lap | Lap | L |
| Reset clock and laps | Reset | R |
| Expand the display | Full screen | — |
| Export lap list | Copy laps as text / Download CSV | — |
Frequently Asked Questions
How do I calculate a lap time by hand?
Subtract the total time of the previous lap from the current total. With times in hh:mm:ss.cc it is easiest to convert both to seconds first. For example, if lap 5 was taken at 03:25.60 (205.60 s) and lap 4 at 02:58.10 (178.10 s), then \( t_{\text{lap},5} = 205.60 - 178.10 = 27.50 \) s, that is 00:27.50. Convert back by dividing: 3600 for hours, 60 for minutes.
What is the difference between a lap time and a split time?
A lap time covers only the segment between two consecutive lap presses, while a split usually refers to the cumulative time at a given point — which this tool calls the total. If you run 4 x 400 m, each 400 m duration is a lap time; the clock reading after each one is the split. Some watches call cumulative values "cumulative splits", so terminology varies by brand.
Does the stopwatch keep counting if I close the tab or shut down my browser?
Yes, if Keep counting across page reloads is checked. The state is stored with a wall-clock timestamp, so when you reopen the page the elapsed time is extended by however long you were away — the clock effectively ran while the browser was closed. Unchecking the box (or using incognito mode, where storage may be blocked) reverts to a stopwatch that resets on every reload.
How accurate is a browser stopwatch compared to a physical one?
The clock itself is very accurate: times come from high-resolution timestamps and are independent of screen refreshes, so a running tab still counts correctly in the background. The practical limit is your reaction time pressing Start or Lap — typically 0.1–0.3 s. For official competitions, record attempts, or any result that must be legally certifiable, always use a certified timing device and human timekeepers.
How do I convert hh:mm:ss.cc into seconds or decimal hours?
To get seconds: \( s = h \times 3600 + m \times 60 + \text{sec} + \tfrac{cc}{100} \). So 00:01:05.20 is \( 1 \times 60 + 5.20 = 65.20 \) s. For decimal hours, divide the total seconds by 3600: 3672 s is about 1.02 h. This is useful for billing or training logs, and a dedicated hours-to-decimal converter does it in one step.
Can I delete or correct just one lap without losing the others?
No — the Reset button clears the entire clock and the whole lap table at once; individual laps cannot be removed or edited. If you pressed Lap a moment too early or too late, simply continue and note which lap is off when you review the export. To fix a mistaken run, copy or download the laps first, then reset and redo the set.
Why are the keyboard shortcuts Space, L and R not working?
The shortcuts are ignored on purpose while you are typing in an input, textarea or select field, so they never interfere with other tools on the page — click on an empty part of the page and try again. They are also skipped when Ctrl, Cmd or Alt is held, and keys differ on non-QWERTY layouts. The on-screen buttons always work as a fallback.