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dB Converter

In Mode, pick Convert level to dB or Convert dB to level, set Quantity type and Decibel unit, enter Value, and press Convert for the results.

What this converter does

In Mode, choose Convert level to dB or Convert dB to level. Convert level to dB takes a level such as 100 mW and returns 20 dBm; Convert dB to level runs the relationship in reverse, returning 100 mW for 20 dBm.

Select Quantity type from Power, Voltage, Current, Frequency or Sound pressure, and a matching Decibel unit from dBm, dBW, dBV, dBmV, dBμV, dBu, dBμA, dBHz, dBSPL or dB. Enter Value and an optional Reference level.

The form computes only when the button is pressed. Results appear in three cards below the button: Decibels, Level and Reference level. Copy writes a result and its unit to the clipboard. Clear resets the form. Everything runs in the browser and nothing is uploaded.

The dB formula

A decibel compares a level with a reference on a logarithmic scale. For power and frequency the multiplier in front of log10 is 10; for voltage, current and sound pressure it is 20.

Worked through, 100 mW against the 1 mW reference gives dBm = 10 × log10(100 mW / 1 mW) = 20 dBm, and 10 V against 1 V gives dBV = 20 × log10(10 V / 1 V) = 20 dBV. Sound pressure is measured against 20 uPa, so 200 uPa gives dBSPL = 20 × log10(200 uPa / 20 uPa) = 20 dBSPL.

With Decibel unit: dBu and Value: 0.7745966692414834, the reference level is 0.7745966692414834 V, giving dBu = 20 × log10(0.7745966692414834 V / 0.7745966692414834 V) = 0 dBu.