Stopwatch workspace
Prepare
You’re ready to start
Set the rhythm, then use the primary timer control when you are ready.
Protect your attention
You’re ready to focus
Choose a duration or start with the defaults. Scenery stays optional and local to this device.
Laps
SceneryNo scenery
Saved only on this device.
Use this result
Share the current inputs or ask ChatGPT to explain the calculation in context.
What does this calculator estimate?
Starting at 0:00 and pressing lap at 1:23.45 records lap 1 at 1:23.45; the next lap measures from there. Elapsed time = current time - start time.
- Elapsed time is measured in milliseconds and displayed as minutes:seconds.hundredths (Wikipedia).
- Lap times record the interval between lap presses.
- Stopwatch precision depends on the device clock and event-loop timing.
What a stopwatch measures
A stopwatch records elapsed time from start to stop, and laps capture the interval between presses — essential for timing workouts, experiments, and processes where split times matter.
Limitations to watch for
Browser timing uses the system clock; background-tab throttling can affect precision. The tool is accurate to hundredths for normal use, not a certified instrument for official timing.
How to use it in practice
Start at the beginning of the activity, press lap at each checkpoint, and stop at the end. Review laps to see where time went. Reset between runs.
['Press start to begin timing.', 'Press lap at each checkpoint.', 'Stop, review laps, and reset.']
How this calculator works
Formula
Elapsed time = current time − start time, measured in milliseconds and displayed as minutes:seconds.hundredths. Lap times record the interval between lap presses.
Worked example
Starting at 0:00 and pressing lap at 1:23.45 records lap 1 at 1:23.45; the next lap measures from there.
Assumptions to verify
- The browser tab remains active.
- Millisecond-level timing from the system clock is sufficient.
- Laps are recorded in sequence.
Frequently asked questions
How does the stopwatch work?
It measures elapsed time from start to stop and records laps between presses, displayed to hundredths of a second.
What are laps?
Interval times recorded between lap presses — so you can compare splits within a single run.
How accurate is it?
Accurate to hundredths of a second for normal use, based on the system clock. Not a certified instrument for official timing.
Why might it drift?
Background-tab throttling can affect browser timers — keep the tab visible for precise timing.
Can I use it for workouts?
Yes — lap intervals are ideal for circuits and interval training.
What's the difference from a countdown?
A countdown runs from a set time down to zero; a stopwatch runs up from zero.
How do I reset?
Press reset after stopping — the display returns to zero for the next run.
Cite this tool
BoringToolsKit. “Stopwatch.” boringtoolskit.com/stopwatch/ (reviewed 2026-08-25). Free to reference in articles, syllabi, and answer posts with a link.
Privacy: Inputs and results stay in this browser. Any future sponsored recommendation or advertisement will be clearly labeled and kept separate from the calculation.