The physical length of one wavelength of coax is:
Coax length, in feet = (984/Frequency) * Velocity Factor

The physical length of one quarter-wavelength of
coax is:
Coax length, in feet = (246/Frequency) * Velocity Factor

For example:
A Quarter wavelength of RG-58/U (VF = 0.66) at
7.025Mhz would be 23.11 feet long.

Coaxial Cable Specifications - 1

Notes:

1. * = Double shielded Coax
2. # = Silver plated centre conductor and shield
3. Centre conductor is copper or tinned copper
   except where indicated by #
4. Insulation dielectric Codes PE: Polyethylene FP: Foam Polyethylene TF: High Temperature Teflon
5. Jacket Material Codes PE: Polyethylene PV: PVC
   NC: Non-contaminating FG: Fiberglass
6. VF = Velocity factor of coax (eg 0.66 = 66%)
7. pf/ft = Capacitance (in pf) per foot
8. Attenuation/100ft = coax attenuation per 100ft at 10Mhz
9. Diameters for centre conductor, insulation and jacket are used for selecting proper connector
   (BNC, PL259, etc.)

Coaxial Cable Specifications - 2