Time

What is a Second?

The second is the base SI unit of time, defined by the cesium-133 atomic transition frequency.

Overview

The second is the base SI unit of time. Since 1967, it has been defined by atomic physics: the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom. This makes the second extraordinarily reproducible — modern atomic clocks based on optical transitions can keep time to a few parts in 10¹⁸. The second is the foundation of all time measurements: the minute (60 s), the hour (3,600 s), the day (86,400 s). It is also fundamental in physics — speeds (m/s), accelerations (m/s²), frequencies (Hz = 1/s), and Planck's constant all reference the second. International civil time, GPS, and the internet's time synchronization all depend on cesium-based atomic seconds. The second relates to the millisecond (1,000 ms = 1 s), the microsecond, and the nanosecond.

Symbol
s
Category
Time
Plural
seconds

Convert Second to all units

Live result
s
Millisecond1,000 msMinute0.016667 minHour0.000278 hDay0.00001157 dWeek0.000001653 wkMonth3.803e-7 moYear3.169 × 10^-8 yrDecade3.169 × 10^-9 decCentury3.169 × 10^-10 c

Relationship to Other Time Units

1 s equals

Visual reference for how the second relates to other time units. Each row links to the full converter for that pair.

1 s=1,000 ms1 s=0.016667 min1 s=0.000278 h1 s=0.00001157 d1 s=0.000001653 wk1 s=3.803e-7 mo1 s=3.169 × 10^-8 yr1 s=3.169 × 10^-9 dec1 s=3.169 × 10^-10 c

When Is the Second Used?

  • Everyday timekeeping
  • Scientific and engineering measurements
  • Sports timing (100 m sprint in ~10 s)
Real-world examples

A blink takes 100–400 ms. Heartbeat at rest ~1 s. The 100 m sprint world record is 9.58 s (Usain Bolt).

Tips for Using the Second

  • 60 s = 1 minute; 3600 s = 1 hour; 86,400 s = 1 day.
  • For sub-second intervals use ms (milliseconds), µs (microseconds) and ns (nanoseconds).
  • The symbol is s (lowercase). "sec" is informal.

Common Mistakes

  • Writing S instead of s for the second.
  • Confusing second of time with second of arc in astronomy.
  • Assuming microsecond and millisecond are similar — 1 ms = 1000 µs.

Convert Second to Other Time Units

Second to Millisecond
1 s = 1,000 ms
Second to Minute
1 s = 0.016667 min
Second to Hour
1 s = 0.000278 h
Second to Day
1 s = 0.00001157 d
Second to Week
1 s = 0.000001653 wk
Second to Month
1 s = 3.803e-7 mo
Second to Year
1 s = 3.169 × 10^-8 yr
Second to Decade
1 s = 3.169 × 10^-9 dec
Second to Century
1 s = 3.169 × 10^-10 c

Convert Other Units to Second

Millisecond to Second
1 ms = 0.001 s
Minute to Second
1 min = 60 s
Hour to Second
1 h = 3,600 s
Day to Second
1 d = 86,400 s
Week to Second
1 wk = 604,800 s
Month to Second
1 mo = 2,629,746 s
Year to Second
1 yr = 31,557,600 s
Decade to Second
1 dec = 315,576,000 s
Century to Second
1 c = 3,155,760,000 s

FAQ About the Second

3 questions
What does the Second (s) measure?
The second measures time. The second is the base SI unit of time, defined by the cesium-133 atomic transition frequency.
When is the Second used?
The second is used in: Everyday timekeeping; Scientific and engineering measurements; Sports timing (100 m sprint in ~10 s). A blink takes 100–400 ms. Heartbeat at rest ~1 s. The 100 m sprint world record is 9.58 s (Usain Bolt).
How accurate are conversions involving the Second?
All conversions on Units Converter use NIST SP 811 and BIPM reference values, accurate to 8 significant figures.