Wavelength and Frequency Calculator

Convert between the wavelength and frequency of an electromagnetic wave in free space using the speed of light, c = lambda x f.

This wavelength and frequency calculator is for radio amateurs, RF and antenna designers, physics students, and anyone working with light or electromagnetic waves. If you need the wavelength of a radio frequency to cut an antenna to length, or the frequency that matches a known wavelength, this tool converts between the two instantly using the speed of light. It suits homework on the electromagnetic spectrum just as well as a quick check on the bench.

Every electromagnetic wave in free space travels at the speed of light, about 299,792,458 metres per second. Wavelength and frequency are tied together by that speed: c = wavelength x frequency. So a higher frequency means a shorter wavelength, and the other way around. The calculator lets you pick which one you know. Enter a frequency in megahertz and it returns the wavelength in metres by dividing the speed of light by the frequency; enter a wavelength in metres and it returns the frequency. Because the speed of light is a constant, the conversion is exact for waves travelling through a vacuum or, very nearly, through air.

FM radio around 100 megahertz is a familiar case. Dividing the speed of light by 100 megahertz gives a wavelength of about 3 metres, which is why FM antennas are sized in metres rather than centimetres. Going the other way, a 2 metre wavelength - the name of a popular amateur radio band - corresponds to a frequency of about 150 megahertz. Shorter wavelengths mean higher frequencies: a microwave oven near 2,450 megahertz has a wavelength of only about 12 centimetres.

The physics is identical worldwide, but the radio bands allocated to each use are not. The exact frequencies set aside for FM broadcast, amateur radio, Wi-Fi, and mobile networks are decided by national and regional regulators, so a band that is legal to transmit on in one country may be restricted in another. This calculator gives the pure physics relationship; always check your local spectrum rules before transmitting. Note too that waves slow down in materials like glass, water, or coaxial cable, so the wavelength inside a medium is shorter than the free-space figure shown here.

• Forgetting the units. This tool uses megahertz and metres; mixing in hertz or centimetres without converting gives answers off by large factors.
• Applying the free-space result inside a cable or material. Signals travel slower there, so the real wavelength is shorter by the velocity factor.
• Confusing wavelength with antenna length. Practical antennas are often a half or a quarter of a wavelength, not a full one.
• Assuming the speed of light applies to sound. Sound is a mechanical wave with a completely different, much slower speed; this formula is only for electromagnetic waves.
• Rounding the speed of light too aggressively for precise RF work, where small differences shift the result.

There are no deadlines here, but there is a practical caution: before transmitting on any frequency, confirm it is allocated for your use and that you hold any license your country requires. Antennas cut from a wavelength should account for the velocity factor of the wire or element and for end effects, so treat the calculated wavelength as the starting point and trim to tune. For coaxial cable and waveguides, apply the medium's velocity factor rather than the free-space number.

• Wavelength - Reference (retrieved 2026-06-11)