Physics

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Attenuation Calculator.

Calculate power attenuation in decibels, with optional length normalization.

On-device calculationNo signup
01

Set your values

Results update as you type.

attenuationDb: 3.0103

attenuationDb

0.000000
attenuationPerLength: 0.030103

attenuationPerLength

0.000000

Use Cases

Evaluate signal loss in a transmission line

Determine how much power is lost in a cable or fiber by comparing input and output power. Useful for troubleshooting or verifying system performance.

Example: Input power 10 W, output power 5 W, length 100 m gives 3.01 dB total, 0.0301 dB/m.

Compare attenuation per meter of different materials

Normalize attenuation by length to compare the loss characteristics of different cables or materials regardless of their total length.

Example: A 50 m cable with 2 dB loss has 0.04 dB/m, while a 100 m cable with 3 dB loss has 0.03 dB/m.

Frequently Asked Questions

How do I calculate attenuation in decibels?
Enter the input power and output power in watts. The calculator computes attenuation as 10 times the log10 of the ratio of input power to output power. If you provide a path length in meters, it also normalizes the attenuation per meter.
What does length normalization mean?
Length normalization divides the total attenuation in dB by the path length in meters, giving attenuation per meter (dB/m). This is useful for comparing the loss characteristics of different materials or cables of varying lengths.
Can I use this calculator for optical fiber or RF cables?
Yes, this calculator works for any system where you know the input and output power in watts. It is commonly used for optical fibers, RF cables, and other transmission lines to determine signal loss.

Tips & Common Mistakes

Tips

  • Ensure both power values are in watts and positive. If output power is greater than input, the calculator will show a negative attenuation (gain).
  • For accurate length normalization, measure the actual path length in meters, not just the cable length if there are bends or extra routing.
  • Use consistent units: if you have power in milliwatts, convert to watts first to avoid errors.
  • Remember that attenuation in dB is logarithmic, so a 3 dB loss means half the power, and 10 dB means one-tenth.

Common Mistakes to Avoid

  • Forgetting to convert power from milliwatts or microwatts to watts before entering values.
  • Entering output power as a percentage of input power instead of an absolute power value.
  • Confusing total attenuation with attenuation per meter when length is provided; the calculator gives both, so check which one you need.

Last updated: August 13, 2026