Divide by 1,000
A millisecond is one thousandth of a second, so converting is just shifting the decimal point three places left. 1,500 ms is 1.5 s; 250 ms is 0.25 s. To go back the other way, multiply seconds by 1,000.
Common values
| Milliseconds | Seconds | What it is |
|---|---|---|
| 16.67 ms | 0.01667 s | One frame at 60 FPS |
| 100 ms | 0.1 s | Feels instant in a UI |
| 250 ms | 0.25 s | Typical human reaction time |
| 500 ms | 0.5 s | One beat at 120 BPM |
| 1,000 ms | 1.0 s | One second |
| 60,000 ms | 60 s | One minute |
Two handy shortcuts from the same divide-by rule: frame time is 1000 / FPS (60 FPS → ~16.7 ms), and beat time is 60000 / BPM (120 BPM → 500 ms).
Where the conversion goes wrong
- ms is not µs. "ms" means milliseconds (thousandths); "µs" means microseconds (millionths), a 1,000× difference. In code,
setTimeout(1000)waits one second, not one microsecond. - Timestamps in ms vs s. JavaScript's
Date.now()returns milliseconds, but a Unix timestamp is in seconds. Feeding one where the other is expected lands you in 1970 or the year 50,000. - Rounding. Floating-point math means 1 ÷ 1000 can print as 0.00099999…. For anything precise, keep integers (work in nanoseconds) and convert once at the end.
Common questions
How many milliseconds are in a second?
Exactly 1,000. A millisecond is one thousandth of a second, so to convert milliseconds to seconds you divide by 1,000. For example, 500 ms is 0.5 s.
How do I convert milliseconds to seconds?
Divide the number of milliseconds by 1,000, which is the same as moving the decimal point three places to the left. So 2,500 ms becomes 2.5 s.
What is the difference between a millisecond and a microsecond?
A millisecond (ms) is one thousandth of a second; a microsecond is one millionth. A microsecond is 1,000 times shorter than a millisecond, so mixing up ms and the microsecond symbol causes a 1,000-fold error.
