To calculate the element length of a halfwave dipole this calculator is based on the formula Wavelength = Speed of Light / Frequency.

However as electricity travels slower through copper than space, I have reduced the velocity factor Vf by about 0.951 before converting it into a 1/2 wavelength.

Length of Element (L)
Frequency Velocity Factor
1/2 Wave Length in MM
Mhz Vf