Millisecond vs Microsecond: What's the Difference?
A millisecond is 1,000 microseconds. See what each unit measures in practice, how to tell them apart in a timestamp, and where the confusion costs you.
A millisecond is 1,000 microseconds. One thousandth of a second against one millionth.
| Unit | Symbol | In a second | Written as |
|---|---|---|---|
| Millisecond | ms | 1,000 | 0.001 s |
| Microsecond | µs | 1,000,000 | 0.000001 s |
What Each One Actually Measures
Milliseconds are the unit of things humans notice. A blink is about 100-400 ms. Perceptible input lag starts around 100 ms. A fast web request is 50-200 ms. When a product team argues about latency, they argue in milliseconds.
Microseconds are the unit of things machines notice. Memory access is tens to hundreds of nanoseconds, so microseconds cover a few thousand of those. Context switches, syscall overhead, and high-frequency trading latency all live here. No human perceives a microsecond.
Telling Them Apart in a Timestamp
This is where the difference costs real time. A Unix timestamp gives no unit — you have to infer it from the digit count:
- 10 digits — seconds (
1735824179) - 13 digits — milliseconds (
1735824179567) - 16 digits — microseconds (
1735824179567890)
Read a millisecond timestamp as seconds and you land in the year 56,000. Read a microsecond value as milliseconds and your duration is 1,000× too long. The [Unix timestamp converter](/tools/unix-timestamp) shows which interpretation gives a sensible date.
The µ Symbol
Microsecond is properly written µs, using the Greek letter mu. Plain ASCII contexts write us, and some logs use usec. All three mean the same thing. ms is never microseconds, though it gets typed that way by mistake constantly.
Which Unit Belongs Where
- API response times, page load, animation frames — milliseconds
- Database query internals, lock contention, network round trips inside a datacentre — microseconds
- CPU instructions, cache hits — nanoseconds, a further 1,000× down
Reporting a number without its unit is the actual bug. A dashboard showing "latency: 420" is unreadable. See [milliseconds vs microseconds vs nanoseconds](/blog/milliseconds-vs-microseconds-vs-nanoseconds) for the full ladder.