⏲️ Free Online Stopwatch - Precise Stopwatch with Lap Timer & Milliseconds
Professional online stopwatch - completely free! Measure time with millisecond precision, track lap times, record split intervals, and use fullscreen mode. Perfect for sports timing, fitness tracking, productivity measurement, racing events, and scientific experiments. Works in any browser - no download required.
⌨️ Keyboard Shortcuts: Space Start/Stop | L Lap | R Reset
📊 Lap Times (0)
No laps recorded yet. Start the stopwatch and click "Lap" to record times.
📐 Stopwatch Time Calculation Formulas
1. Elapsed Time Calculation
Example: Start: 10:30:15.50, Current: 10:32:45.75 → Elapsed = 2 min 30.25 sec
2. Lap Time (Interval) Calculation
Example: Previous lap: 1:30.50, Current lap: 3:15.25 → Lap time = 1:44.75
3. Milliseconds to Time Conversion
4. Average Lap Speed
⏱️ Stopwatch vs Countdown Timer
| Feature | Stopwatch | Countdown Timer |
|---|---|---|
| Direction | Counts UP from 00:00:00 | Counts DOWN to 00:00:00 |
| Starting Point | Always zero | User-defined duration |
| Purpose | Measure elapsed time | Time limit/deadline |
| Setup Required | None - just start | Set target time first |
| Alarm | No (measures open-ended) | Yes (alerts when done) |
| Lap/Split Times | Yes (core feature) | Not typically |
| Best For | Racing, sports, tracking | Cooking, workouts, limits |
🏃 Common Stopwatch Applications
| Activity | What to Measure | Why Use Stopwatch |
|---|---|---|
| Running/Track | Race time, lap splits | Precise timing for performance tracking |
| Swimming | Lap times, total time | Monitor pace and improvement |
| Cycling | Segment times, intervals | Training zone adherence |
| HIIT Workouts | Exercise/rest intervals | Ensure proper timing |
| Presentations | Speech duration | Stay within time limits |
| Productivity | Task completion time | Time tracking and estimation |
| Cooking | Precise timing steps | Technique perfection |
| Gaming Speedruns | Level/game completion | Compare against records |
| Science Labs | Reaction rates, processes | Experimental accuracy |
| Music Practice | Practice session duration | Track daily practice time |
🔵 Understanding Lap Time vs Split Time
Lap Time (Interval Time)
Definition: Time taken for a single lap or segment
Calculation: Current Split - Previous Split
Use: Compare performance between segments
Example: In a 4-lap race, lap 2 took 1:45, lap 3 took 1:52 - lap 3 was 7 seconds slower
Split Time (Cumulative Time)
Definition: Total elapsed time from start to current point
Calculation: Current Time - Start Time
Use: Track progress toward total time goals
Example: After 3 laps, total time is 5:23 (3 laps × ~1:48 average)
Practical Example - 5K Race
| Kilometer | Split Time | Lap Time | Interpretation |
|---|---|---|---|
| 1st km | 5:30 | 5:30 | Started strong |
| 2nd km | 11:15 | 5:45 | Slowed 15 seconds |
| 3rd km | 17:00 | 5:45 | Maintained pace |
| 4th km | 22:30 | 5:30 | Second wind! |
| 5th km | 27:45 | 5:15 | Strong finish |
📖 How to Use the Online Stopwatch
Basic Operation
- Start: Click "Start" button (or press spacebar)
- Stopwatch begins counting from 00:00:00.00
- Stop: Click "Stop" to pause timing
- Resume: Click "Start" again to continue from stopped time
- Reset: Click "Reset" to return to 00:00:00.00
Recording Laps
- Start the stopwatch
- When completing a lap/segment, click "Lap" (or press L key)
- Lap is recorded with:
- Lap number: Sequential count (Lap #1, #2, etc.)
- Lap time: Duration of that specific lap
- Split time: Total elapsed time at that point
- Stopwatch continues running - record as many laps as needed
- All lap times visible in scrollable list below
Keyboard Shortcuts
- Spacebar - Start/Stop toggle
- L - Record lap (while running)
- R - Reset stopwatch
Fullscreen Mode
- Click "Fullscreen" button for large display
- Perfect for: races, public timing, presentations
- Press Esc to exit fullscreen
❓ Frequently Asked Questions
A stopwatch measures elapsed time from a starting point. Common uses:
- Sports & Athletics: Race timing, lap splits, training intervals
- Fitness: Workout duration, HIIT intervals, rest periods
- Productivity: Time tracking, task duration measurement, Pomodoro technique
- Cooking: Precision timing for techniques (blanching, searing, etc.)
- Science: Reaction timing, process duration in experiments
- Public Speaking: Practice speech timing, presentation duration
- Gaming: Speedrun timing, level completion records
- Music: Practice session tracking, tempo measurement
Accuracy: ±10 milliseconds under normal conditions
Technical details:
- API used: JavaScript `Performance.now()` - provides microsecond precision
- Update rate: Display refreshes every 10ms (100 times per second)
- Timing method: Calculates elapsed time from system clock, not simple counting
- Self-correcting: Compensates for JavaScript execution delays
Accuracy factors:
- ✅ Sufficient for: Sports timing, workouts, general use, productivity tracking
- ⚠️ Not suitable for: Scientific precision requiring sub-millisecond accuracy
- 📉 Degrades with: Heavy system load, browser throttling, old hardware
Real-world performance: Accurate enough to time 100m sprint (±0.01s error), track workout intervals, measure productivity periods.
They measure different things:
| Type | Measures | Formula | Use Case |
|---|---|---|---|
| Lap Time | Single segment duration | Current Split - Previous Split | Compare individual laps |
| Split Time | Cumulative total from start | Current Time - Start Time | Track total progress |
Marathon example:
- 10K split: 45:00 (total time to 10K mark)
- 10K lap: 45:00 (first 10K took 45 minutes)
- 20K split: 1:32:00 (total time to 20K)
- 20K lap: 47:00 (second 10K took 47 minutes - slowed by 2 min)
This stopwatch records both! Each lap entry shows interval time (lap) and cumulative time (split).
Yes! Full keyboard control:
| Key | Function | When Available |
|---|---|---|
| Spacebar | Start/Stop toggle | Always |
| L | Record lap | While running |
| R | Reset | When stopped |
| Esc | Exit fullscreen | In fullscreen mode |
Why use keyboard shortcuts?
- Hands-free: Control while cooking, exercising, or with messy hands
- Faster: Quicker than clicking, especially during races
- Accessibility: Easier for users who prefer keyboard navigation
- Multi-tasking: Control stopwatch while using other applications
Yes! Continues accurately even when not visible.
Background behavior:
- ✅ Browser minimized: Stopwatch keeps running accurately
- ✅ Tab in background: Timing continues uninterrupted
- ✅ Switch to other apps: Stopwatch maintains precision
- ✅ Lock screen (mobile): Continues on most devices
- ❌ Close tab: Stopwatch stops and resets
- ❌ Browser crash: Timing lost
How it works: Uses system `Performance.now()` timestamp, not frame-based counting. Calculates elapsed time by comparing current time vs start time, so browser state doesn't affect accuracy.
Best practice: Keep browser tab open for important timing. For critical events, run multiple stopwatches as backup.
Current options for saving lap times:
Method 1: Screenshot
- Windows: Win + Shift + S
- Mac: Cmd + Shift + 4
- Captures visual record of all lap times
Method 2: Print to PDF
- Press Ctrl+P (Windows) or Cmd+P (Mac)
- Select "Save as PDF" as printer
- Saves entire page including lap times
Method 3: Manual Copy
- Select lap times with mouse
- Copy to clipboard
- Paste into spreadsheet, notes, or document
Method 4: Video Recording
- Use screen recording software
- Records entire timing session
- Perfect for races or events
📚 Official Timing & Standards Resources
Time Standards & Precision:
- NIST Time & Frequency Division - U.S. official time standard
- BIPM Time Metrology - International time measurement standards
- ISO 8601 - International time format standard
- MDN Performance.now() - High-resolution time API documentation
Sports Timing Standards:
- World Athletics - Official athletics timing standards
- World Aquatics (FINA) - Swimming timing regulations
- UCI - Cycling timing standards