Online Stopwatch

How to use the stopwatch

• Start / Stop: the same button starts and stops the count. After stopping it reads Resume, and pressing it continues from where you left off.
• Lap: records the time so far without stopping. Each lap adds a row to the table, newest at the top.
• Reset: clears the time and all laps.
• Keyboard: Space starts and stops, L records a lap and R resets. Click an empty part of the page first if the shortcuts don't respond.

The display shows minutes, seconds and hundredths (for example 03:47.10). After an hour, hours are added in front (1:02:15.40). There is no upper limit: the stopwatch can run for days.

The current time and laps are saved in your browser, so an accidental reload or a closed tab doesn't lose a long timing. Reopen the page and the stopwatch shows the full elapsed time, still running if it was running.

Lap time versus total time

The lap table shows two numbers for every lap. Total is the stopwatch reading when you pressed Lap. Lap time is how long that lap alone took — the total minus the previous total. Coaches often call the total a split. Here is how three laps of a run would look:

Once you have three or more laps, the fastest lap is shown in green and the slowest in red, so you can see at a glance whether you kept an even pace or faded at the end.

How accurate is a browser stopwatch?

The stopwatch measures time by reading your device's clock when you press Start and again for every update, rather than adding up ticks. That means the reading stays correct even if the browser slows the page down in a background tab — the number may update less often, but it is never behind when you look at it.

The display shows hundredths of a second, but the biggest source of error is usually the person pressing the button. Starting and stopping by hand adds your reaction time at both ends. For fair comparisons — two runners, two attempts — use the same person and the same method each time.

Two other things to know:

• Clock changes don't affect it. Elapsed time is measured on the universal clock behind your device's local time, so a stopwatch running through the 2 a.m. change on November 1 shows the true elapsed time, not an hour more or less.
• Don't change your device's clock while timing. Setting the time by hand during a run would change the result. Automatic time updates are normally tiny corrections.

Your device keeps its clock right using the Network Time Protocol. The National Research Council of Canada runs public time servers (time.nrc.ca and time.chu.nrc.ca) and says NTP can be accurate to a few milliseconds on a local network.

Timing your activity: Canada's movement guidelines

The Canadian 24-Hour Movement Guidelines for adults aged 18 to 64 recommend at least 150 minutes a week of moderate to vigorous aerobic activity, muscle-strengthening activities at least twice a week, and several hours of light activity, including standing. They also recommend keeping sedentary time to 8 hours or less a day, with no more than 3 hours of recreational screen time, and breaking up long periods of sitting as often as possible.

The stopwatch is an easy way to log activity minutes. Some ways to reach 150 minutes in a week:

Use Lap to separate the parts of a workout — warm-up, main set, cool-down — or to time each interval of a run–walk. The guidelines are for the general adult population; people with health conditions should follow the advice of their own health professional.

Stopwatch or timer?

A stopwatch counts up from zero and answers "how long did that take?" A timer counts down from a time you choose and tells you when it's over. Use the stopwatch to measure a run, a speech rehearsal, a phone call or how long a task really takes. Use the online timer when you already know the length — a 12-minute boil or a 5-minute break — and the alarm clock when you need to be told at a time of day.

Canada's official time

If you need to start timing on an exact second — for example, to check a clock — the National Research Council of Canada provides the country's official time from its atomic clocks:

• Web clock: nrc.canada.ca/en/web-clock shows the official time in every Canadian time zone.
• Telephone talking clock: 613-745-1576 in English and 613-745-9426 in French. It announces Eastern Time every ten seconds, followed by a tone that marks the exact moment, and ticks every second in between. Each call hears three announcements. Calls from outside the Ottawa area are long distance, and the NRC notes that a satellite hop on the line can add a quarter of a second.
• CHU shortwave radio: the NRC also broadcasts time signals continuously by radio.