Pick your Calculation Type and Quantity Type, then enter a Power Ratio (P1/P2), Voltage Ratio (V1/V2), Decibel Value, Power, or dBm Value — the Decibel Calculator works out your Power Gain (dB), Voltage Gain (dB), Power Ratio, and Voltage Ratio so you can stop doing logarithmic math by hand.
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Power Gain (dB)
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Voltage Gain (dB)
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Power Ratio
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Voltage Ratio
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dBm
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Power
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The 10 log formula (dB = 10 log₁₀(P₁/P₂)) is used for power quantities like watts, while the 20 log formula (dB = 20 log₁₀(V₁/V₂)) is used for field quantities like voltage. This is because power is proportional to the square of voltage.
To convert dB to a ratio, use the antilog function: For power ratios, ratio = 10^(dB/10). For voltage ratios, ratio = 10^(dB/20). For example, 10 dB equals a power ratio of 10:1 and a voltage ratio of approximately 3.16:1.
dBm is a unit of power measurement referenced to 1 milliwatt (0.001 watts). It's calculated using the formula: dBm = 10 log₁₀(P/0.001), where P is the power in watts. For example, 1 watt equals 30 dBm.
No, you cannot add or subtract dB values directly like regular numbers because decibels use a logarithmic scale. You must first convert them back to linear ratios, perform the arithmetic operation, then convert back to dB.
A 3 dB increase represents approximately double the power (actually 10^(3/10) = 1.995 times). Similarly, a 6 dB increase is about 4 times the power, and a 10 dB increase is exactly 10 times the power.
When the same signal experiences both voltage and power changes, the power gain in dB is twice the voltage gain in dB. This is because power is proportional to voltage squared, so dB_power = 2 × dB_voltage.
Common references include dBm (1 milliwatt), dBW (1 watt), dBV (1 volt), and dBμV (1 microvolt). Each uses the same logarithmic principles but with different reference points for measurement.