Radio waves, like all electromagnetic waves, travel at the speed of light, and their wavelength and frequency are linked by a simple relationship: wavelength times frequency equals the speed of light. That means a higher frequency always means a shorter wavelength, and knowing one value immediately gives the other. Antenna builders use this constantly, because an antenna’s efficient size is a fraction of the wavelength, often a half or a quarter, so the frequency of a band determines the physical size of the antenna that serves it. This calculator converts in both directions, taking a frequency in megahertz to a wavelength in metres, or a wavelength in metres to a frequency in megahertz, using the exact speed of light constant.
Quick Answer: Enter a frequency in megahertz and click Frequency to Wavelength, or enter a wavelength in metres and click Wavelength to Frequency.
Free Online Tool
Wavelength / Frequency Calculator
Wavelength and frequency from c = λf, in MHz and metres.
How to Use the Wavelength / Frequency Calculator
- Decide which quantity you know: the frequency in megahertz, or the wavelength in metres.
- Enter the known value, checking the unit carefully, since megahertz and gigahertz differ by a factor of one thousand.
- Click the conversion button for the direction you need.
- Read the result, which is given in the complementary unit with three decimal places.
- For antenna work, halve or quarter the wavelength result to estimate half wave or quarter wave antenna lengths.
Key Features
- Frequency to wavelength conversion using the exact speed of light, 299,792,458 metres per second.
- Wavelength to frequency conversion in the reverse direction with the same constant.
- Megahertz and metre units, matching the conventions of amateur and broadcast radio work.
- Three decimal precision, enough for antenna sizing without false precision.
- Instant local calculation for band planning and antenna design.
Best Practices and Tips
- Convert gigahertz figures to megahertz first by multiplying by one thousand, since this calculator expects megahertz input.
- Remember that a half wave antenna for a band is half the wavelength result, and a quarter wave antenna is a quarter of it.
- Account for the velocity factor of real antenna wire, which shortens a practical antenna slightly below the free space calculation.
- Use the wavelength result to sanity check a band: a three metre wavelength belongs near one hundred megahertz, in the FM broadcast region.
Common Mistakes to Avoid
- Entering a frequency in gigahertz as if it were megahertz, which shrinks the wavelength result by a factor of one thousand.
- Confusing wavelength with antenna length. An antenna is usually a fraction of a wavelength, not the full wavelength.
- Forgetting that the relationship uses the speed of light in free space, while signals in cable travel slower.
Frequently Asked Questions
What is the relationship between wavelength and frequency?
Wavelength times frequency equals the speed of light. For radio waves in free space, that speed is 299,792,458 metres per second. Dividing the speed by the frequency gives the wavelength, and dividing it by the wavelength gives the frequency, which is why one value always determines the other.
Why is this useful for antennas?
An antenna resonates best when its length is a simple fraction of the wavelength, most commonly a half or a quarter wavelength. Knowing the wavelength for a frequency therefore tells you directly how long an antenna for that frequency should be, before adjusting for real world factors.
What is a velocity factor?
Signals travel slower in wire and cable than in free space, typically at around two thirds to ninety five percent of light speed depending on the material. A practical antenna is therefore slightly shorter than the free space calculation suggests, and the velocity factor of the material gives the correction.
Does this work for light as well as radio?
Yes, the same relationship governs all electromagnetic waves, from radio through visible light. For visible light the wavelengths are measured in nanometres rather than metres, but the formula is identical, with frequency in the hundreds of terahertz.