There are 86400 seconds in a day.

The story behind the answer

True. A standard day has 24 hours, each hour 60 minutes, each minute 60 seconds: 24 × 60 × 60 = 86,400 seconds. Another way: there are 3,600 seconds in an hour; 24 × 3,600 = 86,400.

Fun context: the second in the SI system is defined by precise vibrations of the cesium-133 atom, and modern clocks keep time with that atomic standard. Because Earth’s rotation isn’t perfectly steady, timekeepers occasionally insert a leap second, making a rare 86,401-second day (or, hypothetically, 86,399). Memory tip: chant “24-60-60,” or think “24 hours × 3.6k seconds/hour = 86.4k seconds.”