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. Be very careful to realize that at frequencies far from DC, factors like skin depth and effective
inner and outer conductor diameters may be significantly different than the physical measured values, and that can significantly affect real
world results. Therefore, be sure to consult manufacturers' published data before making a final decision. I leave it to other sources to provide
the complex equations needed to precisely model coaxial cables.
Braided Flexible Coax
SemiRigid Coax
a = 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.

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.

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.

Note: V has the same length units as
c.

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

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

Equations for coaxial cable attenuation used to be offered here, but while redesigning this page and attempting to verify the equations,
I discovered (or probably rediscovered) that theoretical values versus published measured values for realworld cable varied a lot at every
frequency. RG6 coax, for example, can have a loss at 1 GHz ranging from a little over 5 dB/100 feet to nearly 10 dB/100 feet,
depending on the dielectric type, actual conductor and dielectric diameters, and it seems very importantly, the construction of the outer shield
conductor. A single layer of loosely woven braid versus a one or more dense layer(s) of braid and one or more layer(s) of metal foil versus
semirigid versus hardline coaxial cable makes calculation using a simple, onesizefitsall equation impossible.
Therefore, I have removed the equations I used to have and instead recommend that you visit
coaxial cable manufacturers' websites and consult their published data and decide what
value of attenuation per foot, meter, etc., is most appropriate for your realworld applications.

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
