Hertz, written Hz, measures how many complete cycles occur each second. One kilohertz is 1,000 Hz, one megahertz is 1,000,000 Hz, and one gigahertz is 1,000,000,000 Hz. To find how long one cycle takes, divide 1 by the frequency in hertz; the answer is in seconds.
Before converting a number, identify what repeats. A vibrating object, a repeating animation and a regularly recurring pulse can all have a frequency. The same unit can describe different events, so matching the numbers does not make the events equivalent.
What counts as one cycle?
A cycle is one complete repetition of the pattern. For an ideal pendulum, a journey from the leftmost position to the rightmost position and back to the left is one cycle. The one-way journey is only half a cycle. Counting both directions as separate cycles would double the answer.
In a repeating wave, choose corresponding points: one crest to the next crest, for example. A crest followed by a trough does not complete the pattern. This definition matters more than which point you choose, because a consistent full-cycle count is what makes the frequency meaningful.
The NIST frequency reference defines frequency as the rate of a repetitive event and relates it to cycle duration. For a simple arithmetic example, 24 complete cycles during 6 seconds give 24 ÷ 6 = 4 Hz. If the spacing varies, that calculation describes an average over those six seconds.
The Hz, kHz, MHz and GHz conversion ladder
Each step up this ladder represents a unit 1,000 times larger. Converting to that larger unit makes the numerical value smaller; converting downward makes it larger. The underlying frequency stays unchanged.
| Unit | Symbol | Equivalent in Hz |
|---|---|---|
| Hertz | Hz | 1 |
| Kilohertz | kHz | 1,000 |
| Megahertz | MHz | 1,000,000 |
| Gigahertz | GHz | 1,000,000,000 |
For Hz to kHz, divide by 1,000: 7,500 Hz = 7.5 kHz. Reverse that calculation by multiplying: 7.5 kHz × 1,000 = 7,500 Hz. For MHz to Hz, multiply by one million: 2.75 MHz = 2,750,000 Hz.
You can also move between prefixed units directly. A frequency of 0.006 GHz equals 6 MHz because 0.006 × 1,000 = 6. Those same 6 MHz equal 6,000 kHz and 6,000,000 Hz. Moving from GHz all the way to kHz crosses two steps, so multiply by 1,000,000.
Keep the capitalization: kHz, MHz and GHz, following the SI prefix symbols listed by NIST. In SI notation, a lowercase m means milli, while an uppercase M means mega. Thus mHz and MHz differ enormously. Writing the unit beside every intermediate result makes such transcription mistakes easier to catch.
Convert frequency to period in seconds
The period is the time taken by one complete cycle. Frequency counts cycles per second; period describes seconds per cycle. For a steady repeating event, the two quantities are reciprocals:
Period in seconds = 1 ÷ frequency in Hz.
Frequency in Hz = 1 ÷ period in seconds.
These reciprocal formulas require a positive frequency or period. Zero frequency has no finite repeating period, so do not divide by zero.
At 8 Hz, one cycle takes 1 ÷ 8 = 0.125 seconds. A cycle lasting 0.04 seconds corresponds to 1 ÷ 0.04 = 25 Hz. A slower example works the same way: a period of 5 seconds gives 0.2 Hz, meaning one cycle every five seconds, rather than a fraction of an unfinished event.
Doubling frequency halves the period. Increasing from 8 Hz to 16 Hz changes the period from 0.125 seconds to 0.0625 seconds. This is different from a prefix conversion: finding period changes which quantity you are describing, while changing Hz to kHz merely rewrites the same frequency.
Use milliseconds without losing a factor of 1,000
One second contains 1,000 milliseconds, written ms. Combining that conversion with the reciprocal gives two convenient formulas:
Period in ms = 1,000 ÷ frequency in Hz.
Frequency in Hz = 1,000 ÷ period in ms.
For 250 Hz, calculate 1,000 ÷ 250 = 4 ms. Check it in seconds: 4 ms = 0.004 seconds, and 1 ÷ 0.004 = 250 Hz. For a 20 ms cycle, 1,000 ÷ 20 = 50 Hz. Using 1 ÷ 20 without converting milliseconds would instead give a value in cycles per millisecond.
There is a useful shortcut when frequency is already in kHz: period in ms = 1 ÷ frequency in kHz. Thus 2.5 kHz gives 0.4 ms. Verify by converting 2.5 kHz to 2,500 Hz and calculating 1,000 ÷ 2,500. Both routes must agree.
Keep frequency separate from other specifications
Hz does not measure loudness. A frequency value describes repetition, not how strong a sound is. Likewise, GHz cannot by itself be converted to a download rate in megabits per second. Data transfer depends on how information is represented and carried, not just a cycle count.
A rate in revolutions per minute can be divided by 60 to give revolutions per second: 180 rpm corresponds to 3 rotations per second. Calling that 3 Hz requires defining one complete revolution as the repeating cycle. It does not tell you the speed of a point along its circular path.
For musical pulse counting, see our guide to finding a song’s BPM. For the size of a turn rather than how often it happens, use the degrees and radians guide. These describe related ideas with different quantities.
Check the answer before using it
Write the starting unit, choose a prefix conversion or reciprocal, then label the result. Keep extra digits until the last step. Multiplying frequency in Hz by period in seconds should give 1 for a steady cycle; with milliseconds, the product should be 1,000.
Ordinary multiplication and division are sufficient for these examples. If you prefer a handheld tool, you can browse scientific calculators on Amazon. The most useful habit is still writing the unit beside the number rather than trusting an unlabeled display.
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