A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is equal to 1000 nanoseconds or of a millisecond. Because the next SI prefix is 1000 times larger, measurements of 10−5 and 10−4 seconds are typically expressed as tens or hundreds of microseconds. Examples 1 microsecond (1 μs) – cycle time for frequency (1 MHz), the inverse unit. This corresponds to radio wavelength 300 m (AM medium wave band), as can be calculated by multiplying 1 μs by the speed of light (approximately ). 1 microsecond – the length of time of a high-speed, commercial strobe light flash (see air-gap flash). 1 microsecond – protein folding takes place on the order of microseconds. 1.8 microseconds – the amount of time subtracted from the Earth's day as a result of the 2011 Japanese earthquake. 2 microseconds – the lifetime of a muonium particle 2.68 microseconds – the amount of time subtracted from the Earth's day as a result of the 2004 Indian Ocean earthquake. 3.33564095 microseconds – the time taken by light to travel one kilometre in a vacuum 5.4 microseconds – the time taken by light to travel one mile in a vacuum (or radio waves point-to-point in a near vacuum) 8.01 microseconds – the time taken by light to travel one mile in typical single-mode fiber optic cable 10 microseconds (μs) – cycle time for frequency 100 kHz, radio wavelength 3 km 18 microseconds – net amount per year that the length of the day lengthens, largely due to tidal acceleration. 20.8 microseconds – sampling interval for digital audio with 48,000 samples/s 22.7 microseconds – sampling interval for CD audio (44,100 samples/s) 38 microseconds – discrepancy in GPS satellite time per day (compensated by clock speed) due to relativity 50 microseconds – cycle time for highest human-audible tone (20 kHz) 50 microseconds – to read the access latency for a modern solid state drive which holds non-volatile computer data 100 microseconds (0.1 ms) – cycle time for frequency 10 kHz 125 microseconds – common sampling interval for telephone audio (8000 samples/s) 164 microseconds – half-life of polonium-214 240 microseconds – half-life of copernicium-277 260 to 480 microseconds - return trip ICMP ping time, including operating system kernel TCP/IP