Stopwatch Timer
Online stopwatch with lap times. Accurate timing for workouts, study, and activities. Features digital and analog displays with split time recording.
Formula
Elapsed = ฮฃ running intervals (10 ms resolution) | Lap split n = Lapโ โ Lapโโโ
The stopwatch accumulates elapsed time in 10-millisecond ticks and formats it as mm:ss.cc, so the display resolves to a hundredth of a second. Each lap records the total elapsed time at the moment you press it; the split for a lap is that reading minus the previous one, which is why lap 3 of a run showing 01:12.40 after a lap 2 at 00:47.10 took 25.30 seconds.
Worked Examples
Example 1: Workout Intervals
Problem:Time a 30-second sprint.
Solution:Click Start. Watch display until 00:30.00. Click Pause. Rest.
Result:Accurate interval training
Example 2: Productivity
Problem:Track time spent on a task.
Solution:Click Start when beginning work. Click Pause when taking a break. Total time shows productive hours.
Result:Time tracking
Example 3: Race Splits
Problem:Record lap times for a runner.
Solution:Click Start at gun. Click Lap every time runner passes line. Review list for individual lap performance.
Result:Split analysis
Frequently Asked Questions
How accurate is this online stopwatch?
This stopwatch updates every 10 milliseconds (centi-seconds) and uses your browser's internal clock. It is accurate enough for workouts, cooking, and study sessions. However, for professional sports or scientific experiments requiring microsecond precision, specialized hardware is recommended.
Does it work if I switch tabs?
Modern browsers throttle background tabs to save battery, which can sometimes affect visual updates of timers. However, this stopwatch calculates time based on the system clock difference, so the elapsed time remains accurate even if the display lag occurs while the tab is hidden.
What are laps?
Laps allow you to record intermediate times without stopping the main timer. This is useful for tracking splits in a race (e.g., each lap of a track) or timing different segments of a workout.
Can I measure hours?
Yes, the format MM:SS.ms automatically scales. While the display emphasizes minutes and seconds, it will continue tracking accurately as hours accumulate.
Does it require internet?
Once the page is loaded, the stopwatch runs entirely using local JavaScript code. You can even disconnect from the internet and it will continue to work.
Can I save my times?
Currently, your lap times are displayed in the list below the timer. You can manually copy them. Refreshing the page will reset the timer.
What is the difference between a stopwatch and a timer?
A stopwatch counts UP from zero (measuring elapsed time). A timer (or countdown) counts DOWN from a set time to zero (measuring remaining time).
How do I reset the stopwatch?
Click the 'Reset' button (refresh icon). This will stop the timer, set it back to 00:00.00, and clear all recorded laps.
What is the difference between a split time and a lap time?
A split is cumulative: it records total elapsed time from the start at each mark, so the final split equals the finish time. A lap is the interval since the previous mark, so the laps sum to the finish time. Converting between them is arithmetic, since subtracting consecutive splits gives laps and running a total of laps gives splits. Coaches read splits against a target pace and laps to find the segment that slowed.
Why do two people timing the same race by hand disagree?
Hand timing adds human reaction latency twice, once at the start and once at the stop, and the two delays do not cancel because the start is anticipated while the stop is reactive. The scatter is on the order of a couple of tenths of a second, which is why hand times are traditionally recorded to coarser precision than electronic timing and why events use several timekeepers and average their readings.
Background & Theory
Timing Mechanics:
- Mechanical: Uses a mainspring and balance wheel. Precision limited by mechanics (typically 1/5 or 1/10 sec).
- Quartz: Uses an electronic oscillator regulated by a quartz crystal. Very accurate.
- Software: Uses the device's system clock (CPU cycles). High accuracy but dependent on system resources.
Common Uses:
- Sports: Racing, swimming, motorsports (often with photo-finish technology).
- Laboratory: Measuring chemical reactions or physics experiments.
- Industrial: Time-and-motion studies to optimize manufacturing.
- Fitness: HIIT, Tabata, and interval training.
- Cooking: Exact timing for brewing coffee or baking.