Online Stopwatch

Your time

Press Start to begin timing

Start, Stop and Lap are under the display. The space bar starts and stops; L takes a lap. It keeps going if you switch tabs, and picks up again if you reload in this browser.

The working

Seconds = hours × 3600 + minutes × 60 + seconds + hundredths ÷ 100

A lap time is the total at that lap minus the total at the lap before. The average lap is the total at the last lap ÷ the number of laps. Pace is time ÷ distance; speed is distance ÷ time.

Worked examples

• A reading of 12:34.56 is 12 × 60 + 34 + 0.56 = 754.56 seconds. Over 5 laps that is 754.56 ÷ 5 = 150.912 s, or 02:30.91 a lap.
• Five 400 m laps in 12:34.56 is 2 km, so the pace is 754.56 ÷ 2 = 377.28 s, or 06:17 per km, and the speed 2 ÷ (754.56 ÷ 3600) = 9.54 km/h.
• Laps of 1:31.20, 1:29.85 and 1:30.40 add to 04:31.45; the average is 01:30.48 and the spread 1.35 s.

Good to know

Timing well by hand

• Reaction time matters more than the clock. Starting and stopping by hand adds roughly 0.1 to 0.3 s each time, so the hundredths are a guide, not a result.
• Watch the start signal, not the runner. Hand timers start on the flash or the gun, and stop when the torso crosses the line.
• Lap, don't stop. Taking a lap keeps the total running; stopping and starting again loses the gap in between.
• The screen can sleep. The time is worked out from the clock, so it stays right even if the page is in the background, but keep the screen on to see it.
• Not for official records. Races, safety checks and medical timing need a proper timing system.

Questions

Questions people ask about stopwatches

Printout

Your timing sheet

Your laps with totals, the fastest and slowest, and spare rows for event, lane, attempt, timekeeper, device and notes, for timing by hand.

For spreadsheets and code

Check it yourself

hours, minutes, seconds, hundredths = 0, 12, 34, 56
laps = 5
elapsed = hours * 3600 + minutes * 60 + seconds + hundredths / 100
average = elapsed / laps if laps else 0
print(round(elapsed, 2), round(average, 3))  # 754.56 150.912

Spreadsheet: a time typed as 0:12:34.56 in A1 becomes seconds with =A1*86400.

Background

From pocket watch to screen

Stopwatches grew out of 19th-century chronographs, watches with a hand that could be started, stopped and sent back to zero, first made for astronomy and horse racing. Electronic timing replaced hand timing for official records because a thumb is slower than a light beam.

A general timing tool: not for official race results, safety alarms, medical timing or legal time records. It ignores leap seconds, like most clocks.

Sources

Where these rules come from

• NIST: Time and frequency from A to Z
• NIST: Time services
• BIPM: The SI Brochure (the second)