Attenuator / dB ↔ voltage divider calculator

Attenuator / dB Voltage Divider

Design from target attenuation and input impedance (optional load), or analyze an existing divider. Compare with nearest E-series resistors.

Mode

Target attenuation (dB)

Desired input impedance Z_in

Load resistor R_load (optional)

R1 (top resistor)

R2 (bottom resistor)

Invalid input. For design: dB > 0 and Z_in > 0 (and R_load < Z_in·A). For analyze: R1,R2 > 0.

Precision:

R1 (ideal)

R2 (ideal)

Vout/Vin (no load)

Attenuation (no load, dB)

Vout/Vin (with load)

Attenuation (with load, dB)

Input impedance seen by source

Nearest resistor series

R1 (nearest standard)

R2 (nearest standard)

Vout/Vin (rounded)

Attenuation (rounded, dB)

Vout/Vin (rounded, with load)

Attenuation (rounded, with load, dB)

Input impedance seen by source (rounded)

Error vs target (dB)

A = Vout/Vin = R2 / (R1 + R2) (no load). With load R_load, use R2′ = R2 || R_load, then A = R2′ / (R1 + R2′). dB = −20·log₁₀(A).