Electrical reference chart
Decibel Reference Chart
Use this decibel reference chart after the calculator result to document the reference value, ratio type, gain or loss direction, and impedance basis.
Quick reference table
Use this decibel reference chart to remember that 3 dB is about 2x power, 6 dB is about 2x voltage, 10 dB is 10x power, and -3 dB is about half power. Decibels are ratios tied to a reference, so record the power or voltage basis before using the calculator result.
Common decibel ratios
| dB | Power ratio | Voltage ratio | Reference use |
|---|---|---|---|
| 3 dB | about 2x | about 1.41x | Approximate doubling of power |
| 6 dB | about 4x | about 2x | Approximate doubling of voltage |
| 10 dB | 10x | about 3.16x | One decade of power ratio |
| 20 dB | 100x | 10x | One decade of voltage ratio |
| -3 dB | about 0.5x | about 0.71x | Approximate half-power point |
Decibel result context checks
| Calculator result is | Record next | Why it matters |
|---|---|---|
| Power gain or loss | P1, P2, measurement point, and reference condition | A dB value has no meaning without the ratio behind it |
| Voltage gain or loss | V1, V2, and whether impedance basis is the same | The 20 log formula depends on that assumption |
| Negative dB value | Whether the result represents attenuation, loss, or lower measured level | Sign communicates direction, not a separate unit |
| Power-quality note | Meter type, measurement window, and reference value | Measurement setup can change interpretation |
Decibel chart to calculator handoff
| Search or worksheet need | Use this chart for | Open the calculator when |
|---|---|---|
| dB power ratio | Choosing the 10 log formula and checking gain or loss direction | Actual P1 and P2 values need a calculated dB result |
| dB voltage ratio | Checking the 20 log relationship on the same impedance basis | V1, V2, and the measurement basis must be recorded |
| Negative dB value | Confirming that the compared value is below the reference | The sign, reference value, and attenuation note need a worksheet record |
| Power-quality or signal note | Keeping ratio math separate from measurement interpretation | Meter setup, measurement window, and reference values change the conclusion |
How to use this chart
Identify the compared values
Record whether the calculator result compares power, voltage, signal level, attenuation, gain, or another measurement basis.
Confirm the reference
Decibel values need a reference value or ratio, so document what P1, P2, V1, or V2 represents.
Mark gain or loss
After the calculator result, record whether the positive or negative dB value represents gain, loss, attenuation, or level difference.
Formula basis
Power ratio: dB = 10 log10(P2 / P1). Voltage ratio: dB = 20 log10(V2 / V1) when impedance basis is the same.
- P2 and P1 are compared power values.
- V2 and V1 are compared voltage values.
- dB is the logarithmic ratio between the two values.
Worked examples
Convert power ratio to dB
A power ratio of 10 to 1 is 10 log10(10) = 10 dB. The meaning depends on the reference measurement.
Convert voltage ratio to dB
A voltage ratio of 2 to 1 on the same impedance basis is 20 log10(2) = about 6.02 dB.
Related calculators
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.