Millisecond (ms)

The millisecond is a unit of time equal to one thousandth of a second. Its symbol is ms. It is the shortest interval that people encounter by name in everyday life, largely because computing and networking made it a household measurement.

Human perception sets the scale that makes it interesting. The eye fuses separate images into motion somewhere around forty milliseconds apart, which is why cinema at twenty-four frames a second works. Audio is far less forgiving: a delay of more than about ten milliseconds between a musician's action and the sound they hear is enough to disrupt playing, and stereo direction is judged from arrival-time differences between the ears of well under one millisecond.

Network latency is quoted in milliseconds and is the number that determines whether a connection feels responsive. Light travels about three hundred kilometres in a millisecond in fibre, so intercontinental round trips have an irreducible floor: London to New York cannot go below roughly sixty milliseconds no matter how much is spent on equipment. Competitive online gaming, financial trading and video calling are all shaped by that limit.

Reaction time is measured in the same unit. A trained sprinter responds to a starting gun in around 150 milliseconds, and athletics rules treat anything below 100 milliseconds as a false start on the grounds that no human can react faster. Simple visual reaction times in a laboratory typically fall between 200 and 250 milliseconds.

Computing uses milliseconds as the natural unit for anything involving storage or human interaction. A mechanical hard disk seeks in several milliseconds while a solid-state drive answers in a fraction of one, a difference of two orders of magnitude that explains most of the change in how computers feel over the last two decades. Timestamps in most programming environments count milliseconds since the start of 1970.

Photography borrows it for shutter speeds, where a thousandth of a second is a common setting for freezing motion, and physiology uses it for the duration of a nerve impulse, which lasts one to two milliseconds.

One millisecond equals 0.001 seconds, 1000 microseconds, or one 3,600,000th of an hour.

Millisecond conversion table