Decibel Calculator
Convert power or voltage ratios to decibels (dB).
Decibel Converter
Understanding Decibels (dB)
The decibel (dB) is a logarithmic unit that expresses the ratio of two values of a physical quantity, such as power or intensity. It is widely used in acoustics, electronics, and control theory.
Decibel Formulas
For Power Ratios:
dB = 10 * log10(P2 / P1)
For Voltage/Current Ratios:
dB = 20 * log10(V2 / V1) or dB = 20 * log10(I2 / I1)
Where:
• P1, P2 = Power values
• V1, V2 = Voltage values
• I1, I2 = Current values
• log10 = Base-10 logarithm
dB = 10 * log10(P2 / P1)
For Voltage/Current Ratios:
dB = 20 * log10(V2 / V1) or dB = 20 * log10(I2 / I1)
Where:
• P1, P2 = Power values
• V1, V2 = Voltage values
• I1, I2 = Current values
• log10 = Base-10 logarithm
Common Decibel Values
| dB Value | Power Ratio (P2/P1) | Voltage Ratio (V2/V1) |
|---|---|---|
| 0 dB | 1 | 1 |
| 3 dB | 2 | ~1.414 |
| 6 dB | 4 | 2 |
| 10 dB | 10 | ~3.162 |
| 20 dB | 100 | 10 |
| -3 dB | 0.5 | ~0.707 |
| -10 dB | 0.1 | ~0.316 |
Frequently Asked Questions
Why are decibels used?
Decibels are used because they can represent very large or very small ratios in a more manageable way. They are particularly useful for expressing changes in power or amplitude over a wide range, such as in audio or radio frequency applications.
What is the difference between dB and dBm?
dB is a relative unit, expressing a ratio. dBm is an absolute unit, referencing 1 milliwatt (mW). So, 0 dBm equals 1 mW. dBm is commonly used in RF and fiber optic power measurements.