Frequency counts repeating cycles per second; period is the time taken by one cycle. Choose the direction, enter a positive value, and select both units. In frequency-to-period mode the entered value uses the frequency unit; in the reverse mode it uses the period unit.
The reciprocal relationship
For frequency measured in hertz and period measured in seconds:
Convert the entered value to Hz or seconds before taking the reciprocal, then convert the answer to the requested unit. One kHz is 1,000 Hz; one MHz is 1,000,000 Hz; one GHz is 1,000,000,000 Hz. A millisecond is 0.001 seconds and a microsecond is 0.000001 seconds.
Worked conversions
| Starting value | Period per cycle |
|---|---|
| 1,000 Hz | 1 ms |
| 2 kHz | 0.5 ms |
| 2.5 MHz | 0.4 µs |
| 1 GHz | 1e-9 s |
In the reverse direction, a period of 2 ms is 0.002 seconds, so the frequency is 1 ÷ 0.002 = 500 Hz. These are reciprocal conversions, not estimates of a measured signal.
Reading small values
The primary answer uses your selected output unit. The supporting rows also show the frequency in Hz and the period in seconds. Ordinary values show up to six decimal places; very small or large values use scientific notation rounded to seven significant digits so a nonzero answer stays visible. For example, 1e-9 s means one billionth of a second.
Zero frequency has no finite cycle duration, and zero period has no finite reciprocal frequency. Negative values and numbers outside the supported finite range return no answer. The relationship assumes a repeating cycle; it does not describe the duration of an entire recording, an irregular event sequence, or angular frequency in radians per second.
For changing only Hz, kHz, MHz, and GHz, use the frequency unit converter. For ordinary durations, use the time converter.
Sources
- BIPM, The International System of Units, 9th edition, version 4.01 — Table 4 defines hertz as reciprocal second; Table 7 defines the decimal prefixes. The reciprocal conversion follows from those units and the stated periodic-cycle assumption.