Seconds and milliseconds
The second is the SI base unit of time, defined by 9,192,631,770 periods of the caesium-133 hyperfine transition. Every other time unit here is a multiple of the second.
A millisecond is one thousandth of a second. Reaction times, network latency, video frame times and timestamps in software are measured in milliseconds.
Worked example
Convert 1.5 s: 1.5 × 1,000 = 1,500, so 1.5 seconds is 1,500 milliseconds. Likewise 2 s = 2,000 ms.
Estimating in your head
The factor is a power of ten, so just move the decimal point 3 places to the right: 1.5 s = 1,500 ms.
Going the other way
To convert milliseconds to seconds, divide by 1,000 (or multiply by 0.001). The swap button between the boxes opens that page.
How this works
ms = s × 1,000
1 s = 1 s and 1 ms = 0.001 s, both by definition, so the factor is their ratio: 1,000 exactly. Results drop binary floating-point noise beyond 15 significant digits and display at the precision you choose (6 significant figures by default). Copy result copies the full value.
Frequently asked
How many milliseconds are in a second?
1 second = 1,000 milliseconds, exactly. The value follows from the unit definitions, so it never changes.
How do I convert seconds to milliseconds?
Multiply by 1,000. For example, 2 s × 1,000 = 2,000 ms.
What is 10 s in milliseconds?
10 s = 10,000 ms. The table next to the converter lists more common values.
Is the result rounded?
Only on screen. The page computes with the exact definitions and removes floating-point noise past 15 significant digits; pick 3 to 12 significant figures, or use Copy result for the full value.
Sources
- BIPM — The International System of Units (SI Brochure), 9th edition
- NIST SP 811 Appendix B.8 — Factors for units listed alphabetically
- Wikipedia — Gregorian calendar
Reviewed Oct 17, 2026 · test vectors fixtures/units/time/seconds-to-milliseconds/