Time Converter
Time is one of the seven SI base quantities, with the second as the fundamental unit. Time conversions range from the extremely small to the very large: nanoseconds for computing and light-speed calculations, milliseconds for everyday digital interactions and chemical kinetics, seconds as the standard unit, minutes and hours for human-scale activities, days and weeks for calendars, and months, years, decades, and centuries for history and long-term planning. The second is defined by atomic clocks based on cesium atoms and is the most precise time measurement available. Smaller units like nanoseconds are essential in computing; modern processors execute billions of operations per second measured in nanoseconds. Larger units like months and years introduce complexity because they vary: months have between 28 and 31 days, and years vary due to leap years. For practical conversions, this calculator uses the Julian year average of 365.25 days per year, making a month equal to 30.4375 days on average. Converting between time units is essential when working with durations in different contexts, from microsecond-precision timing in laboratories to calculating ages in decades or centuries. This calculator displays twelve time units: nanoseconds through centuries. Enter a value in any field and all others update instantly.
NIST conversion factors
All conversions below use standard NIST-defined factors, with all units expressed relative to the second. Note that months and years use average values.
| Unit | Symbol | Seconds |
|---|---|---|
| Nanosecond | ns | 0.000000001 |
| Microsecond | us | 0.000001 |
| Millisecond | ms | 0.001 |
| Second | s | 1 |
| Minute | min | 60 |
| Hour | h | 3,600 |
| Day | d | 86,400 |
| Week | wk | 604,800 |
| Month (average) | mo | 2,629,800 |
| Year (Julian) | yr | 31,557,600 |
| Decade | dec | 315,576,000 |
| Century | cent | 3,155,760,000 |
Time converter: frequently asked questions
What is the SI unit of time?
The second is the SI base unit of time. All other time units are defined relative to the second. The second is defined by the number of cycles of radiation emitted by a cesium atom and is the most precise time standard available.
Why do months and years have approximate values?
Because months vary in length (28 to 31 days) and years vary due to leap years, these conversions use averages. A month is approximated as 30.4375 days (365.25 days per year divided by 12), and a year is approximated as 365.25 days (the Julian year). Precise conversions depend on the specific month or year.
What is a nanosecond used for?
A nanosecond is one billionth of a second. Nanoseconds are used to measure the speed of light operations, computer processor cycles, and chemical reaction kinetics. Modern computers can execute billions of instructions per second, measured in nanoseconds.
What is the difference between a day and a solar day?
A day in this calculator is 24 hours, exactly 86,400 seconds. A solar day is the actual time it takes Earth to rotate relative to the sun, which is slightly longer due to Earth's orbital motion. For most practical purposes, they are close enough to use interchangeably.
How precise are these conversions?
The SI second is defined exactly. Conversions for minutes, hours, days, weeks are exact. Conversions for months and years use the Julian year average of 365.25 days. All conversions shown are mathematically precise to two decimal places.
Official sources
- NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices.
- NIST Special Publication 330: The International System of Units.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.