Most professional
engineers and technicians will never have the need to calculate the capacitance, inductance, or impedance of a coaxial
cable since they are usually designing systems using welldefined components that are manufactured to exacting specifications.
Students, hobbyists (Ham radio operators), and research types are probably the ones most likely to actually plug
numbers into a calculator. For those people, I present these equations.
Braided Flexible Coax

SemiRigid Coax

Capacitance (C) 
, wherea = outside radius of inner conductor
(inches)
b = inside radius of outer conductor
(inches)
c = speed of light in a vacuum = 299,792 km/s = 186,282 mi/s
ε = dielectric constant = ε_{0} * ε_{r}
ε_{0} = permittivity of free space = 8.85419x10^{12}
F/m
ε_{r} = relative dielectric constant
μ_{r} = relative permeability

Note: a and
b can be in any units of length as long as they are both the same.

Inductance (L) 
Note: a and
b can be in any units of length as long as they are both the same. However,
l must be in the
units shown.

Impedance (Z_{0}) 
Note: a and
b can be in any units of length as long as they are both the same. L
has units of Farads and
C has units of Henries.

Speed of Light (%c) 
Note: V has
the same length units as
c.

Cutoff Frequency 
Note: a and
b must be in units of length shown.

Reflection Coefficient & VSWR 
Note: Γ
is unitless.
VSWR is written as a
VSWR:1 ratio.

Coaxial Cable Attenuation 
Cable attenuation is the sum of the conductor losses and the dielectric losses per the following equations.
Note: While reworking this page I was able to confirm all equations with original
sources except these two, so use them with caution. I cannot recall where I got them.

, where
a = outside diameter of inner conductor
(m)
b = inside diameter of outer conductor (m)
f = frequency (GHz)
Z = impedance (Ω)
tan(δ) = loss tangent
ε_{r} = relative dielectric constant
ρ_{ra} = inner conductor material resistivity
relative to copper
ρ_{rb} = outer conductor material resistivity
relative to copper
Note:
ρ_{r} = 1 for copper,
= 10 for steel

Related Pages on RF Cafe  Coaxial Cable
Specifications  Capacitor Dielectrics & Descriptions
 Dielectric Constant, Strength, &
Loss Tangent  Conductor Bulk Resistivity & Skin
Depths  Coaxial Cable Equations 
Coaxial Cable Specifications 
Coaxial Cable Vendors  Coaxial Resonator  Skin Depth Calculator

Coaxial Connector Usage Chart
