Calculator Inputs
Enter a signal amplitude and a positive reference amplitude. The calculator uses the logarithmic amplitude-decibel relationship.
Plotly Graph
The graph shows how decibel value changes as amplitude grows relative to the chosen reference amplitude.
Formula Used
Main formula:
dB = 20 × log10(A / Aref)
Where A is the measured amplitude and Aref is the reference amplitude.
Equivalent power relationship:
Power Ratio = (A / Aref)2
Power dB = 10 × log10(Power Ratio)
Amplitude-based decibels use 20 instead of 10 because power is proportional to the square of amplitude for many physical systems.
How to Use This Calculator
- Enter the measured signal amplitude.
- Enter the reference amplitude for your experiment or application.
- Optionally add a second comparison amplitude.
- Choose a unit label such as V, Pa, or mm.
- Set precision and graph settings if needed.
- Press Calculate dB to view results above the form.
- Use the CSV or PDF buttons to export the output.
Example Data Table
| Signal Amplitude | Reference Amplitude | Amplitude Ratio | Decibel Value | Interpretation |
|---|---|---|---|---|
| 0.25 | 1.00 | 0.25 | -12.0412 dB | Much lower than reference |
| 0.50 | 1.00 | 0.50 | -6.0206 dB | Half the reference amplitude |
| 1.00 | 1.00 | 1.00 | 0.0000 dB | Equal to reference |
| 2.00 | 1.00 | 2.00 | 6.0206 dB | Double the reference amplitude |
| 4.00 | 1.00 | 4.00 | 12.0412 dB | Strong increase over reference |
FAQs
1) What does amplitude to dB mean?
It converts an amplitude ratio into a logarithmic decibel value. This makes very small and very large changes easier to compare in physics, acoustics, vibration, and electronics work.
2) Why is the formula 20 log10 instead of 10 log10?
Use 20 log10 for amplitude quantities such as voltage, pressure, or displacement. Use 10 log10 for power quantities. The factor changes because power often scales with amplitude squared.
3) Can I use this for sound pressure level studies?
Yes, when you have a pressure amplitude and a matching reference pressure. Make sure both values use the same unit before calculating the decibel result.
4) What happens if amplitude equals the reference?
The ratio becomes 1, and log10(1) equals 0. That means the output is exactly 0 dB, showing no increase or decrease relative to the reference.
5) Can negative or zero amplitudes be entered?
No. The logarithm requires a positive ratio. This calculator validates the input and asks for positive amplitude values to avoid undefined results.
6) Is a 6 dB increase equal to double amplitude?
Approximately yes. Doubling amplitude gives 20 log10(2), which is about 6.0206 dB. The exact number depends on the true amplitude ratio.
7) Why does the calculator also show power ratio?
Many labs and engineering tasks compare both amplitude and power behavior. Showing the equivalent power ratio helps connect the signal result to energy-related interpretations.
8) When should I use a custom reference amplitude?
Use a custom reference whenever your experiment, instrument, or standard is not based on a unit reference. This keeps the decibel result tied to the correct baseline.