A fundamental measurement in radio antenna work is the "half wavelength" (λ/2).
It gives the desired physical length of a Dipole antenna for any operating frequency.
This calculator automatically converts the desired frequency into length (in feet) and gives the overall length and individual leg length (which is a ¼λ).
Use 50 ohm cable such as RG58, RG8X, RG8, RG213, or 75 ohm cable such as RG11, RG59, RG6 or 75 ohm twin ladder line to feed the centre of the dipole.
Be sure to securely solder the feed cable to each leg of the dipole for good electrical contact because the centre of the dipole is a high-current low-voltage point. It is also a good idea to provide some strain relief which can be a simple matter of wrapping the feed cable once around the centre insulator and securing it with a cable tie. Ensure also that the feeder is sealed against water ingress, coax is jokingly, but accuratly, known as a "Self Filling Hosepipe".
Measurements are given in feet, inch, metre and cm for ease of use, choose just one set for your build. Make the legs slightly longer than the calculated length to allow for wrapping around the end insulators, tuning adjustments etc.