Signal Attenuation dB Calculator
Calculate signal attenuation or gain in decibels from an input/output power or voltage pair — supports linear power units (mW/W/µW), direct dBm readings, and voltage ratios, not just a single power-ratio mode.
Input
Output
| Metric | Value |
|---|---|
| No data yet | |
Guides
The Signal Attenuation dB Calculator converts an input/output power or voltage pair into decibels — the standard way signal loss (or gain) is expressed in RF, audio, networking, and cable specs. Unlike a plain power-ratio calculator, it also accepts values already given in dBm and supports a separate voltage ratio mode, so you don't need to convert your readings by hand first.
How to use it
- Choose the ratio type: Power (the default) or Voltage/Amplitude.
- For power, choose the input format:
- Linear power — enter input and output power in mW, W, or µW.
- dBm — enter input and output power directly in dBm (common on signal meters and spec sheets); the calculator simply subtracts them.
- For voltage, enter input and output voltage in V, mV, or µV.
The result shows the gain/attenuation in dB (negative = loss, positive = gain), the output/input ratio, the equivalent power-loss percentage, and the exact formula used.
The formulas
- Power ratio:
dB = 10 × log₁₀(Pout ÷ Pin) - dBm difference:
dB = Pout(dBm) − Pin(dBm)— decibels are already logarithmic, so dBm readings subtract directly instead of needing to be converted back to linear power first. - Voltage ratio:
dB = 20 × log₁₀(Vout ÷ Vin)— the factor is 20, not 10, because power is proportional to voltage squared. Power loss for a voltage ratio assumes equal impedance at both points (Ppower ratio = Vratio²), which is the standard assumption when only voltage is known.
A drop of about 3 dB means the power has roughly halved; 10 dB means a 10× drop; 20 dB means 100×. A positive dB value means the signal was amplified rather than attenuated.
Limitations
This calculator works from power or voltage ratios alone. It doesn't model impedance mismatch, reflections (VSWR), connector loss, or a cable's frequency-dependent attenuation curve — for a real link budget, use manufacturer-specified per-length loss figures at your actual frequency.
Everything runs in your browser; no inputs are sent to a server.
Use it from code
From 3 credits per callREST API
curl -X POST https://api.iotools.cloud/v1/tool/signal-attenuation-db-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"ratioType": "power",
"inputFormat": "linear",
"powerUnit": "mw",
"powerIn": "10",
"powerOut": "5"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `signal-attenuation-db-calculator` tool (Signal Attenuation dB Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.