Frequency converter

Divide by 60, because hertz counts cycles per second and rpm cycles per minute. 3,000 rpm is 50 Hz, 1,800 rpm is 30 Hz, and 7,200 rpm, a common hard-drive speed, is 120 Hz. To go from Hz to rpm, multiply by 60.

Because its speed is locked to the supply frequency. A synchronous motor turns at 120 × f ÷ p rpm, where p is the number of poles, so a two-pole motor runs at 3,000 rpm on 50 Hz mains and 3,600 rpm on 60 Hz. Induction motors run a few percent below this synchronous speed, for example 2,900 rpm on 50 Hz.

Multiply by 2π, about 6.28319: ω = 2πf. 50 Hz is 314.16 rad/s and 1 Hz is 6.2832 rad/s. Both units reduce to “per second”, but a hertz counts whole cycles while a radian per second counts the angle swept, and one cycle is 2π radians.

2 Hz: 120 beats ÷ 60 seconds. Tempo in beats per minute converts to hertz by dividing by 60, so 90 BPM is 1.5 Hz. The same rule applies to heart rate: the American Heart Association's normal adult resting range of 60 to 100 beats per minute is 1 to 1.67 Hz.

1,000. SI prefixes step by 1,000: 1 GHz = 1,000 MHz = 1,000,000 kHz = 10⁹ Hz. Wi-Fi's 2.4 GHz band is 2,400 MHz, and a 3.5 GHz processor clock ticks 3.5 billion times a second. Frequency prefixes are always decimal, never the binary 1,024 used for some memory sizes.

Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 4 worked examples whose answers come from independent sources; for example, “3000 rpm in Hz” is checked against 3000 / 60 = 50.

NIST SP 811 (2008), Guide for the Use of the SI, Appendix B — conversion factors; NIST Handbook 44, Appendix C — General tables of units of measurement.