Stopwatch & Timer

Free online stopwatch and countdown timer

Stopwatch
Timer
00:00:00.00

How Does the Stopwatch & Timer Work?

Switch between Stopwatch and Timer modes using the tabs. The Stopwatch counts up from zero with Start, Stop, Lap, and Reset buttons. Lap records split times while the stopwatch keeps running. The Timer lets you set hours, minutes, and seconds for a countdown. When the countdown reaches zero, an alert sound plays and the display flashes. Both modes provide precise timing with a clean, large digital display that works on any device.

Frequently Asked Questions

How accurate is the online stopwatch?
The stopwatch uses JavaScript's performance timing and updates every 10 milliseconds, providing accuracy suitable for most everyday timing needs.
Can I record lap times?
Yes, click the Lap button while the stopwatch is running to record split times. All laps are displayed in a table below.
Does the timer make a sound when done?
Yes, the countdown timer plays an alert sound and shows a visual notification when the time reaches zero.

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Stopwatch precision, lap timing and reaction lag

A hand-operated stopwatch cannot be more accurate than the person pressing it — about 0.2 to 0.3 seconds per press. This is why hand timing in athletics is rounded to a tenth of a second and never accepted for records, which require fully automatic timing to the hundredth.

Timing precision by method

MethodResolutionReal accuracy
Hand-held stopwatch0.01 s displayed±0.2–0.3 s, dominated by human reaction
Browser performance.now()—Deliberately coarsened to 0.1–1 ms to prevent timing attacks
Browser Date.now()1 msSubject to system clock adjustments and NTP steps
Athletics fully automatic timing0.001 sGun-triggered start, photo-finish stop; records require it
Swimming touchpad0.01 sOfficial standard for world records
Formula 1 transponder timing0.001 sLoop-triggered, no human in the path
Video at 60 fps16.7 msA cheap and surprisingly good upgrade on hand timing

Lap versus split — they are not the same

TermMeasuresExample over 4 laps
Lap timeThe duration of that lap alone1:02, 1:05, 1:04, 1:01
Split timeCumulative elapsed time at that point1:02, 2:07, 3:11, 4:12
Sector timeA named subsection of a lapUsed in motorsport to locate where time was lost

Why hand timing is biased fast

The start and stop presses do not carry equal error. At the start, the timekeeper reacts to a visual or audible signal, adding a delay of roughly 0.2 s. At the finish they can anticipate the runner arriving and press early. The two errors do not cancel — anticipation at the finish is usually larger than reaction at the start, so hand times come out systematically fast. This is why World Athletics adds 0.24 seconds to a hand time when converting it to an estimated automatic time for sprints up to 200 m, and 0.14 seconds for longer distances. A hand-timed 11.0 in the 100 m is really about 11.24.

Getting a defensible time without professional equipment

  1. Film it at 60 fps or higher and count frames. A phone at 240 fps gives you 4 ms resolution for free and removes the human entirely.
  2. Have the same person start and stop, so at least the bias is consistent between attempts.
  3. Time three attempts and take the median, not the best — the best is the one where you pressed early.
  4. Start on the visual, not the sound, if you are near the start; sound travels 343 m/s, which is 0.03 s per 10 metres.
  5. Record the method alongside the number. A time without its timing method is not comparable to anything.

Reference times, for context

EventWorld recordTiming standard
100 m sprint (men)9.58 s — Usain Bolt, 2009Fully automatic, 0.001 s
100 m sprint (women)10.49 s — Florence Griffith-Joyner, 1988Fully automatic
Marathon (men)Under 2:01Chip and gun timing
50 m freestyle swim (men)Under 21 sTouchpad, 0.01 s
Rubik’s cube singleAround 3.1 sWCA Stackmat, 0.01 s, hands-on-pad start

More questions people ask

How accurate is a stopwatch?

The device itself is accurate to a hundredth of a second, but a human press adds 0.2 to 0.3 seconds of error. That is why hand times are rounded to a tenth and never accepted for official records, which require fully automatic timing.

What is the difference between a lap time and a split time?

A lap time is the duration of one lap on its own. A split time is the cumulative elapsed time at that point in the run. Four laps of roughly a minute each give lap times near 1:00 and splits of 1:00, 2:00, 3:00 and 4:00.

Why are hand-timed race results slower than official ones?

They are usually faster, not slower — a timekeeper can anticipate the finish and press early. World Athletics adds 0.24 seconds to a hand-timed sprint result to estimate the equivalent automatic time.

Can I use a phone stopwatch for official timing?

No. Official athletics, swimming and cubing records all require certified automatic or standardised equipment with a defined trigger. A phone is fine for training and for personal comparison, provided you note that the method was hand timing.

How can I time something precisely without special equipment?

Film it at 60 frames per second or higher and count frames — that gives 16.7 milliseconds of resolution, or about 4 milliseconds at 240 fps, and removes human reaction time from the measurement entirely.

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Answers, not just a number

Short, exact answers to the questions people ask alongside this tool — the number first, then the working.

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