Yagi Element Spacing Calculator
Enter the operating frequency and spacing fraction.
Result
How it is calculated
The tool turns a frequency and a chosen spacing fraction into a physical distance. First the free-space wavelength: λ = 300 ÷ f metres, with f in megahertz (the 300 comes from the speed of light, about 300 million m/s). Then spacing = fraction × λ, where the fraction is the spacing in wavelengths, for example 0.2 for 0.2 λ. It shows the spacing in metres to three decimals, the same spacing in centimetres, and the wavelength itself. Frequency and fraction must both be above zero, and the tool does not limit how large the fraction is. The wavelength is for free space; it does not apply the velocity factor, element diameter or end-effect corrections that affect real element lengths, and it does not tell you which fraction to pick.
Worked example
You are building an antenna for 144 MHz and want the spacing between two elements to be 0.2 wavelengths. The wavelength is 300 ÷ 144 = 2.083 m. Multiplying by 0.2 gives 0.41667 m, which the tool shows as 0.417 m, or 41.67 cm. Mark the elements 41.67 cm apart along the boom. For a reflector at 0.15 λ instead, the spacing would be 0.15 × 2.083 = 0.3125 m, about 31 cm.
Common mistakes
- Entering the frequency in GHz or kHz. The field is megahertz, so 144 MHz is 144, not 0.144; typing 0.144 gives a wavelength of more than 2 km.
- Typing the fraction as a percent. A spacing of 0.2 λ is entered as 0.2, not 20; 20 would mean twenty wavelengths.
- Using the wavelength as an element length. The result is the gap between elements, and a half-wave element is shorter than half this wavelength once end effects and the velocity factor are taken into account.
- Using one spacing fraction for every element. Reflector and directors usually need different gaps, so run the calculator once for each fraction you want.
- Measuring spacing from element ends instead of centres. The distance is between element centres along the boom.
About this calculator
A Yagi-Uda antenna gets its directional gain from a row of parallel elements — a driven element, one reflector behind it, and one or more directors in front — all tuned relative to the operating wavelength λ = c/f. Element spacing, not just length, is what determines how the elements' fields combine constructively in the forward direction.
Typical designs place the reflector about 0.15 to 0.25 λ behind the driven element and directors roughly 0.1 to 0.2 λ apart in front of it — closer director spacing generally raises gain but narrows bandwidth and increases design sensitivity, which is why real antenna designs are usually optimized numerically rather than built from spacing rules alone.
Amateur radio operators and antenna builders use this frequency-to-wavelength relationship as a starting point for laying out element positions before fine-tuning a design in modeling software or on the workbench.
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