Insertion Loss Calculator
Calculate insertion loss from power or voltage measurements — in dB, with a 3-way solver, dB ↔ linear-ratio conversion, and multi-stage cascade summation. 100% runs in your browser.
IL power: 10·log₁₀(Pin/Pout)IL voltage: 20·log₁₀(Vin/Vout)Cascade: Σ IL
Formula: IL = 10 · log₁₀(Pin / Pout). With dBm units, IL = Pin(dBm) − Pout(dBm) directly (e.g. 30 dBm → 27 dBm = 3 dB). Negative values mean gain.
One-click examples
Example results: 1 W → 0.5 W gives 3.0103 dB (half the power lost). 2 V → 1 V gives 6.0206 dB (factor 20, not 10, because it is voltage). Cascade 3 + 2 + 1.5 dB = 6.5 dB total.
Quick reference table
| Insertion loss | Power ratio | Power through | Voltage ratio |
|---|---|---|---|
| 0.5 dB | 1.1220 : 1 | 89.13 % | 1.0593 : 1 |
| 1 dB | 1.2589 : 1 | 79.43 % | 1.1220 : 1 |
| 1.5 dB | 1.4125 : 1 | 70.79 % | 1.1885 : 1 |
| 3 dB | 1.9953 : 1 | 50.12 % | 1.4125 : 1 |
| 3.0103 dB | 2.0000 : 1 | 50.00 % | 1.4142 : 1 |
| 6 dB | 3.9811 : 1 | 25.12 % | 1.9953 : 1 |
| 6.02 dB | 3.9994 : 1 | 25.00 % | 1.9999 : 1 |
| 10 dB | 10.0000 : 1 | 10.00 % | 3.1623 : 1 |
| 20 dB | 100.0000 : 1 | 1.00 % | 10.0000 : 1 |
| 30 dB | 1000.0000 : 1 | 0.10 % | 31.6228 : 1 |
Scope boundary vs Pi/T Attenuator Designer: this tool calculates insertion loss from measured results or Pin/Pout ratios. To design Pi/T attenuator resistor values from a target dB, use Pi/T Attenuator Designer.
Scope boundary vs Distance Attenuation: this tool covers insertion loss of RF-electronic circuits/components. For sound attenuation over distance (acoustics), use Distance Attenuation.
Frequently asked questions (FAQ)
- What is insertion loss?
- Insertion loss (IL) is the power lost when a device is inserted into a transmission path, expressed in decibels (dB). It is calculated as
IL = 10 · log₁₀(Pin / Pout)for power. Example: 1 W in and 0.5 W out gives10 · log₁₀(2) = 3.0103 dB. - What is the difference between insertion loss and return loss?
- Insertion loss measures power lost through the device (transmitted signal), while return loss measures power reflected back toward the source due to impedance mismatch (RL = −20·log₁₀|Γ|). A device can have low insertion loss but poor return loss, or vice versa — they describe different loss mechanisms.
- Why does the power formula use 10·log₁₀ but the voltage formula uses 20·log₁₀?
- Because power is proportional to voltage squared (P = V²/R). Taking the log: log₁₀(V²) = 2·log₁₀(V), which moves the factor 2 in front: 10 × 2 = 20. Both formulas measure the same physical loss when impedances are equal — halving the power (3.0103 dB) also halves the voltage-squared, i.e. voltage drops by √2, and 20·log₁₀(√2) = 3.0103 dB. Identical.
- Can insertion loss be negative?
- Yes. Negative insertion loss means gain — the output exceeds the input, as with an amplifier (a −10 dB "loss" is a 10 dB gain). For passive devices (cables, connectors, filters, attenuators), insertion loss is always zero or positive.
- How do I calculate insertion loss from dBm readings?
- Simply subtract:
IL = Pin(dBm) − Pout(dBm), because dBm is already logarithmic. Example: 30 dBm in and 27 dBm out gives exactly 3 dB of insertion loss — no log math needed. - How do you add insertion loss in a cascade of stages?
- Add the decibel values: ILtotal = Σ ILi. Example: stages of 3 dB + 2 dB + 1.5 dB give 6.5 dB total, which equals an overall power ratio of 4.4668 : 1. Never add the linear ratios — always sum in dB, then convert once at the end if needed.
- What does 3 dB of insertion loss mean?
- It means half the power is lost (a 2 : 1 power ratio; 50% gets through). Precisely, 3.0103 dB equals exactly half power. Similarly, 10 dB means one-tenth of the power remains (90% lost) and 20 dB means one-hundredth remains.
- Is insertion loss the same as attenuation?
- They are related but not identical. Attenuation is the general term for any signal-level reduction (by distance, cable, or components). Insertion loss is specifically the attenuation caused by inserting a device into the line. This calculator computes insertion loss from measured Pin/Pout; to design resistor values for a Pi/T attenuator, use our Pi/T Attenuator Designer instead.
- Does the voltage formula require matched impedance?
- Yes —
IL = 20·log₁₀(Vin/Vout)is only valid when the input and output impedances are equal. If they differ, measure power in watts and use the power formula10·log₁₀(Pin/Pout), which is always correct. - How do I convert insertion loss in dB to a linear ratio?
- Power ratio = 10dB/10 and voltage ratio = 10dB/20. Example: 10 dB converts to a power ratio of 10 : 1 and a voltage ratio of 3.1623 : 1. Going the other way: dB = 10·log₁₀(power ratio) = 20·log₁₀(voltage ratio).
See also
Pi/T Attenuator Designer
Design Pi/T attenuator resistor values from a target dB — then measure the result here.
Design Pi/T attenuator resistor values from a target dB — then measure the result here.
Free Space Path Loss Calculator
Free-space path loss (FSPL) for RF link budgets — complements your chain-loss analysis.
Free-space path loss (FSPL) for RF link budgets — complements your chain-loss analysis.
Feedline Lab
Coax cable, connector, and SWR loss — the most common insertion-loss sources in RF installations.
Coax cable, connector, and SWR loss — the most common insertion-loss sources in RF installations.
Free tool by NRTechStudio