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Insertion Loss Calculator

Created by Purnima Singh, PhD
Reviewed by Steven Wooding
Last updated: Jan 18, 2024

The insertion loss calculator determines the insertion loss in signal transmission by comparing the input and output power (or voltage) levels.

Please continue reading to learn the definition of insertion loss and the formula to calculate it. You will also find an example of how to calculate the insertion loss using this tool.

Let us start with understanding what insertion loss is.

What is insertion loss?

When we insert a network between the source and load of a circuit (see figure 1), a part of the power is either reflected by the network towards the source or is dissipated within the network. This results in a reduction of the power delivered to the load.

So what is the definition of insertion loss? Insertion loss is a parameter that measures this loss or attenuation in power (or signal strength). It is expressed in decibels (dB) and is crucial when designing microwave and RF transmission circuit components, e.g., filters, equalizers, etc.

For example, in power line communication (PLC) systems, we use impedance matching networks between PLC modems and power line channels. These impedance matching networks are made from passive elements like resistors, capacitors, and inductors that dissipate some power. Hence, the power delivered to the receiver is reduced, and we get insertion loss.

Measuring insertion loss using a two-port network.
Fig 1: Two-port network inserted between source and load.

Another important performance parameter associated with the transmission circuits is the VSWR (Voltage Standing Wave Ratio).

How to calculate insertion loss – Insertion loss formula

To find the insertion loss of a 2-port network (for example, an attenuator or a filter), we measure the voltage across the load before and after the insertion of the network. Then we can calculate the insertion loss in decibels ILIL using the formula:

IL=20 log[V2V1]IL = 20\ \text{log} \left [ \frac{V_2}{V_1} \right ]


  • V2V_2 – Voltage across the load before insertion of the network; and
  • V1V_1 – Voltage across the load after insertion of the network.

As we know that the power delivered is directly proportional to the square of the voltage, i.e., IV2I \propto V^2, we can also use the following formula for insertion loss calculation:

IL=10 log[PLPT]IL = 10\ \text{log} \left [ \frac{P_L}{P_T} \right ]


  • PLP_L – Power delivered to the load before insertion; and
  • PTP_T – Power delivered to the load after insertion.

If you are interested in calculating the loss in signal strength of radiofrequency signal emitted by an antenna, check out our free space path loss calculator.

How to use the insertion loss calculator

Now let us see how to use our calculator to compute the insertion loss if the power delivered to the load before insertion is 12 W and after insertion is 4 W.

  1. Using the drop-down menu, choose to calculate the insertion loss from power delivered to the load.

  2. Enter the values of power before (12 W) and after insertion (4 W) in the respective fields.

  3. The tool will calculate the insertion loss in dB and display the result (4.77 dB).

Alternatively, if you know the voltages before and after the insertion, choose the voltage across load option from the drop-down menu.


How do I calculate insertion loss?

To calculate the insertion loss for a two-port network, follow these instructions:

  1. Measure the power delivered to the load before inserting the two-port network.

  2. Measure the power delivered to the load after inserting the two-port network.

  3. Divide the value from step 1 by that from 2 and take the logarithm of the result.

  4. Multiply the result from step 3 by 10 to get the insertion loss.

What is the insertion loss if 90% of the power is transmitted?

0.46 dB. To arrive at the answer, proceed as follows:

  1. Use the formula for insertion loss: IL = 10 × log (Pi / Pt), where Pi is the incidenct power nad Pt is the transmitted power.
  2. You will get: IL = 10 × log (100 / 90) = 0.46
  3. Hence the insertion loss is 0.46 dB.

What causes insertion loss?

Insertion loss is unavoidable, and it may be due to one of the following reasons:

  • Ohmic loss due to power dissipated in the conductor used to make the transmission line components, i.e., cables, connectors, etc.
  • Poor connection and field termination can also cause a significant loss in transmitted signal strength.
  • Dielectric loss due to the absorption of the signal by the dielectric material that forms the conductor insulation and cable jacket.

How is insertion loss related to frequency?

For a given cable length and specification, the insertion loss is directly proportional to the frequency of the transmitted signal. The higher the frequency, the greater the loss.

Purnima Singh, PhD
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