dB Calculator
Express a power or amplitude ratio in decibels against your chosen reference.
Formula
power: 10 log₁₀(x/x₀); amplitude: 20 log₁₀(x/x₀)
Linear ratio ≈ (10)÷(1) · Level ratio (dB) ≈ 10×log10((10))
How to use
- Choose power/intensity or amplitude.
- Enter positive values in the same unit.
- Read the ratio and its decibel value.
Examples
- A power ratio of 100 or amplitude ratio of 10 gives 20 dB.
Frequently asked questions
When is the factor 20 valid?
When power is proportional to amplitude squared with the same proportionality, such as equal impedances.
Is the result dBm or dB SPL?
Only if you choose the corresponding reference and quantity; this tool supplies no fixed reference.
Can decibels be negative?
Yes. A value below the reference gives a negative dB ratio.
Sources
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