Insertion Loss Calculator — IL = 10 log₁₀(P_in/P_out)
Calculate the insertion loss of a filter, connector, cable, or other passive device in decibels. Enter input and output power (or voltage) values to get the insertion loss in dB and the corresponding power and voltage ratios.
Input type
W
W
Signal power lost by inserting the device into the transmission path
- 1
Power ratio
P_in ÷ P_out = 10 ÷ 1 = 10 - 2
Insertion loss
10 × log₁₀(10) = 1010 dB = 10× power reduction; 3 dB ≈ half power.
How does this calculator work?
Insertion loss IL = 10 × log₁₀(P_in / P_out) dB measures signal power lost by inserting a component into a transmission path. For voltages (equal impedance): IL = 20 × log₁₀(V_in / V_out). Higher dB = more loss. 3 dB ≈ half power; 10 dB = one-tenth power. Enter input and output values to compute IL instantly.
Formula
How this is calculated
Insertion loss (IL) measures the reduction in signal power that occurs when a component such as a filter, attenuator, cable, or connector is inserted into a transmission path. It is expressed in decibels (dB): IL = 10 × log₁₀(P_in / P_out), where P_in is the input power and P_out is the output power. A positive insertion loss means power is lost — 3 dB corresponds to half the power, 10 dB to one tenth, 20 dB to one hundredth.
When measuring voltages rather than powers (and both ports have equal impedance), the power ratio is proportional to the square of the voltage ratio, giving IL = 20 × log₁₀(V_in / V_out). This is the same formula used for voltage gain in amplifier specifications, just applied in the attenuating direction.
Insertion loss is distinct from return loss (how much signal is reflected back) and from attenuation, which is sometimes used interchangeably but technically refers to signal reduction per unit length in transmission lines. For passive devices, insertion loss is always non-negative (no power is created). Ideal components have zero insertion loss; real components always have some due to conductor resistance, dielectric losses, and impedance mismatch.
Frequently asked questions
For connectors and cables, values below 0.5 dB are typical and good; high-quality SMA connectors can achieve < 0.1 dB. For band-pass filters in the pass-band, values below 1–3 dB are usually acceptable. Exact requirements depend on the system budget — in long chains, small individual losses accumulate.
Decibels let you add losses in a chain: if a cable has 2 dB insertion loss and a filter has 1.5 dB, the total loss is 3.5 dB. With linear ratios you would need to multiply (0.63 × 0.71 = 0.45), which is harder to chain. Decibels also compress the very large dynamic range of real RF systems into a manageable scale.
Insertion loss measures how much signal passes through a device (forward loss). Return loss measures how much signal is reflected back toward the source (IL = 10 log(P_in/P_out); RL = -10 log(P_reflected/P_in)). A device can have low insertion loss but poor return loss if it passes signal but also reflects some. Good RF design minimises both.
Also known as
TG we-Calculate Editorial Team. (2026). Insertion Loss Calculator — IL = 10 log₁₀(P_in/P_out) [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/insertion-loss-calculator
TG we-Calculate Editorial Team. "Insertion Loss Calculator — IL = 10 log₁₀(P_in/P_out)." TG we-Calculate. 2026. https://we-calculate.com/calculator/insertion-loss-calculator.
TG we-Calculate Editorial Team, "Insertion Loss Calculator — IL = 10 log₁₀(P_in/P_out)," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/insertion-loss-calculator
@misc{wecalculate_insertion_loss_calculator, title = {Insertion Loss Calculator — IL = 10 log₁₀(P_in/P_out)}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/insertion-loss-calculator}}, year = {2026}, note = {TG we-Calculate} }
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