Dipole Length in Feet = 468 / MHz
Frequency in MHz
I use 14 AWG, copper, THHN wire for my dipoles. I cut them to the length shown in the calculation, then fold them in half to cut them exactly in the middle. Most of my dipoles are fed with RG-8 coax cable. I use a 1:1 baluns from Balun Designs. I hang the dipoles as high as possible, as flat as possible, as straight as possible, and as far away from any buildings, and any metal objects, as possible. An accurately cut dipole, installed as described, should be very close to resonant at the desired frequency.
The ARRL has a good article on dipoles on their web site.