| Seconds (s) | Minutes (min) |
|---|---|
| 1 Second | 0.0166666666667 min |
| 2 Seconds | 0.0333333333333 min |
| 3 Seconds | 0.05 min |
| 4 Seconds | 0.0666666666667 min |
| 5 Seconds | 0.0833333333333 min |
| 10 Seconds | 0.166666666667 min |
| 20 Seconds | 0.333333333333 min |
| 25 Seconds | 0.416666666667 min |
| 50 Seconds | 0.833333333333 min |
| 100 Seconds | 1.66666666667 min |
| Reference | Seconds (s) | Minutes (min) |
|---|---|---|
| A blink of an eye | 0.1 s | 0.00166667 min |
| One heartbeat at rest | 0.83 s | 0.0138333 min |
| Half of a football match | 2700 s | 45 min |
| A full day | 86400 s | 1440 min |
The second is the base unit of time in the International System of Units. Its symbol is s. It is defined by fixing the frequency of the caesium-133 hyperfine transition at exactly 9,192,631,770 cycles per second, so a second is the duration of that many oscillations.
The name records a division that no longer exists in practice. Medieval astronomers divided the hour into sixty minutae primae, first small parts, and each of those into sixty minutae secundae, second small parts. English kept the first as minute and the second as second, leaving the ordinal in the name of a unit almost nobody thinks of as ordinal.
For most of history the second was defined from the rotation of the Earth, as one 86,400th of a mean solar day. That definition failed once clocks became better than the planet: the Earth's rotation is irregular, slowing over centuries from tidal friction and wobbling on shorter timescales. The atomic definition adopted in 1967 severed the link, which is why leap seconds are occasionally inserted to keep civil time aligned with the sun.
Every other time unit is now built on it, and the second underpins most of the rest of the SI as well. The metre is defined through the speed of light in metres per second, the kilogram through the Planck constant which carries a second in its units, and the ampere through the elementary charge per second. Caesium fountain clocks realise the unit to a few parts in ten to the sixteenth, and optical clocks now do better still.
Because atomic clocks keep better time than the planet does, the two have to be reconciled. The Earth's rotation is slowing irregularly, so a day is now a millisecond or two longer than 86,400 atomic seconds, and the difference accumulates. Since 1972 the answer has been the leap second: an extra second inserted at the end of a June or December, announced months in advance, which has happened twenty-seven times. Computer systems handle the repeated timestamp badly enough that outages have been traced to it, and in 2022 the world's metrology bodies voted to abandon the practice by 2035, letting civil time drift from solar time instead.
One second equals 1000 milliseconds, one sixtieth of a minute, or about 0.000277778 hours.
The minute is a unit of time equal to 60 seconds, or one sixtieth of an hour. Its symbol is min. It is not an SI unit but is accepted for use with the SI, and it is one of the very few sexagesimal survivals in ordinary modern life.
The division of the hour into sixty parts comes from Babylonian astronomy by way of Greek and Islamic scholarship. Sixty is a highly composite number, divisible by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 and 60, which means halves, thirds, quarters, fifths and sixths of an hour are all whole numbers of minutes. A decimal hour of a hundred parts would give clean halves, quarters and fifths but no exact third, and a third of an hour is a quantity people actually use.
For centuries the minute was a theoretical division rather than a measured one, because no clock could show it. Mechanical clocks with only an hour hand were normal until the seventeenth century, and it was the pendulum, developed by Christiaan Huygens from Galileo's observation of isochronism, that first made minute-level accuracy ordinary. The minute hand followed the pendulum, not the other way round.
The French Republic tried to abolish it. The decimal time introduced in 1794 divided the day into ten hours of a hundred minutes, each of a hundred seconds. It was mandatory for less than two years, failed because every clock in the country would have needed replacing, and remains the clearest demonstration that metric reform succeeds only where the existing units are genuinely inconvenient.
Modern use is universal and unremarkable. Appointments, cooking times, journey durations, sports periods and billing increments are all in minutes, and the unit sits at a natural human scale: long enough to be a meaningful span of activity, short enough to be planned around without further subdivision.
Its sixtieth-part logic is shared with the circle, and the two meet in navigation. A minute of arc of latitude is one nautical mile, and a ship covering one nautical mile in one minute of time is travelling at sixty knots, which is why an old rule of thumb converts between distance and time on a chart without arithmetic. Music divides time the same way. Tempo is given in beats per minute, from a funeral march near 60 to dance music at 120 or more, and the metronome that Maelzel patented in 1815 fixed that convention in print. In both fields the minute is short enough to feel and long enough to count.
One minute equals 60 seconds, one sixtieth of an hour, or about 0.000694444 days.