Stopwatch | Laps, Splits & Average Time
Use a precise online stopwatch with lap tracking, split times, fastest and slowest lap detection, average lap time, pace estimates, session summaries, and CSV export.
Current Split
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Pace Calculator
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Pace/mi
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No laps recorded
Start the stopwatch and press Lap or the L key
What Is the Stopwatch?
Most stopwatches show one number: total elapsed time. Useful, but it doesn't show how fast each individual interval was. That's what split time is for. Press Lap at the end of each interval and the split column shows exactly how long that rep took, independent of everything before it.
performance.now() updates every 16 ms and the display refreshes at 60 fps via requestAnimationFrame. You get centisecond accuracy — which matters when timing sprint repeats where a half-second difference is meaningful.
Beyond raw timing, there's a statistics layer: fastest split, slowest, average, and standard deviation. Enter a target lap time and every split gets colour-coded against it. Enter a lap distance and the pace column converts every split to min/km or min/mile. Export everything as CSV for spreadsheet analysis.
Stopwatch Formula and Method
Split time (lap time) = elapsed at current lap − elapsed at previous lap.
Total elapsed = running wall-clock time from Start press to current moment.
Average lap = Σ(all split times) ÷ number of laps.
Standard deviation of laps = √(Σ(split − average)² ÷ n) — low SD means consistent pacing, high SD indicates variable effort.
Pace per km = split time (seconds) ÷ distance per lap (km); pace per mile = split time (seconds) ÷ distance per lap (miles).
Target delta = split time − target lap time (negative = faster than target, positive = slower).
Timing precision: performance.now() provides sub-millisecond resolution; display updates at 60 fps via requestAnimationFrame for smooth centisecond rendering.
How to Use
- 1
Press Start or hit Space. The centisecond display (MM:SS.cc) starts immediately using performance.now(). No warm-up, no countdown.
- 2
Press L (or click Lap) at the end of each interval. The split table updates in real time: elapsed, split duration, and gap versus your target.
- 3
Click the note icon on any lap row to add a name or label. Notes appear in the CSV export — useful when timing multiple athletes in sequence.
- 4
Set a Target Lap time in MM:SS format before or during timing. After each lap, the delta column shows green (faster) or red (slower) — no mental arithmetic.
- 5
Enter a distance per lap and the pace column calculates automatically. A 400m rep in 72 seconds shows as 3:00/km. Switch the unit toggle for miles.
- 6
Read the statistics summary after at least two laps: fastest, slowest, average, and standard deviation. Low SD means consistent pacing across all reps.
- 7
Click Download CSV to export: lap number, split, elapsed, target delta, pace, notes. Opens directly in Google Sheets or Excel with no setup needed.
- 8
Press Reset to clear all laps and return to zero. Your target lap and distance settings are preserved for the next session.
Stopwatch Example
A swimming coach times six athletes in sequence — Start, then L as each swimmer finishes. Notes label each lap with the athlete's name. After six laps: splits 58.3 s to 1:04.7, average 1:01.2, SD 2.4 s. Target was 62 seconds. Four athletes hit it (green), two didn't (red). The CSV pastes directly into the season tracking sheet.
A trail runner doing five 2 km laps sets a target of 11:00. Splits: 10:52, 10:59, 11:04, 11:03, 10:57. SD is 5 seconds — excellent consistency. Without the lap timer, only the total time (54:55) is known. The split sequence tells the real story.
Understanding Stopwatch
Split Time vs Elapsed Time: Why the Distinction Matters
Elapsed time always increases — it's the total running time from Start to now. Split time is different: how long did this specific interval take, independent of everything before it?
A 400m runner on their fourth rep in 86 seconds is fading. Their elapsed total hides it; their split sequence shows it: 80, 82, 83, 86. Both columns are recorded for every lap.
Standard Deviation: The Pacing Number Coaches Actually Use
Average lap time tells you what you did. Standard deviation tells you how consistently you did it. A runner with a 90-second average and SD of 2 seconds is well-paced.
The same average with SD of 8 seconds means they surged or faded badly. Range (fastest vs slowest) hides this — one outlier inflates it. SD captures the full distribution. Target: SD under 3% of your average split.
CSV Export: From Session Data to Progress Tracking
Each CSV row is one lap: number, split, elapsed, target delta, pace, and notes. Import directly into Google Sheets or Excel — column headers included, no setup needed.
Stack CSVs from multiple sessions by date to chart how splits tighten over a season. For teachers running timed assessments, the CSV creates an objective record for progress reports.
Keyboard Shortcuts: Eyes on the Athlete, Not the Screen
Space toggles Start and Pause. L records a lap. R resets when stopped. These three keys cover everything. Run an entire multi-athlete session by feel — Space at the start signal, L as each finishes.
Your eyes should be on the performance, not the laptop. The screen is consulted afterward.
Pace Calculator for Runners, Cyclists, and Swimmers
A split time in MM:SS isn't always enough — you need pace per km or mile to compare across different interval distances. Enter the distance per lap and every split converts automatically.
A 400m rep in 72 seconds is 3:00/km. A 1500m swim in 22:30 is 1:30/100m. No mental arithmetic during the session review.
Frequently Asked Questions
What's the difference between split time and elapsed time?
Elapsed time is total running time from Start — it always increases. Split time is the duration of one interval: current elapsed minus previous lap elapsed. Both are recorded for every lap.
What are the keyboard shortcuts?
Space toggles Start and Pause. L records a lap split while running. R resets to zero when stopped. All three work without a mouse — essential when your eyes need to stay on the athlete.
How accurate is the browser stopwatch?
performance.now() provides sub-millisecond resolution. The display refreshes at 60 fps. Human reaction time (150–250 ms for a manual lap press) is the practical accuracy limit, not the timer itself.
How do I export the lap data?
Download CSV exports all laps: number, split, elapsed, target delta, pace, and notes. Headers included — open directly in any spreadsheet app. Copy gives the same data as plain text. Export before resetting.
What does standard deviation of laps tell me?
SD measures how much splits vary around the average. Low SD (2–3 s for 400m reps) means consistent pacing. High SD means variable effort. Aim for SD under 3% of your average split.
Can I time multiple athletes with one stopwatch?
Yes. One lap per athlete — press L as each finishes. Add their name as a note on the lap row. Split column shows each individual time. Export CSV for records. Works best when athletes finish within a few seconds of each other.
Does the stopwatch keep running if I switch browser tabs?
Yes. Elapsed time stays accurate in background tabs — the app records the wall-clock start time and calculates elapsed as current time minus start. Lap recording requires the tab to be active when you press L.
How do I use the target lap feature?
Enter your goal split in MM:SS format. After each lap, the delta column shows the difference: green minus means faster, red plus means slower. Set it before your session for real-time pass/fail feedback on every split.
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