Decibel Converter

How to use

1. 1Pick what to convert: ratio to dB, dB to ratio, dBm and watts, dBW and watts, or combine gains.
2. 2For the ratio and gain modes, choose whether the quantity is power (10 x log10) or amplitude such as voltage, current, or pressure (20 x log10).
3. 3Type your value. Gains are positive, losses are negative, and ratios must be greater than zero. Commas and scientific notation are accepted.
4. 4Read the result tiles, including the alternate interpretation and the dBm or dBW equivalents where relevant.
5. 5In the combine mode, list each stage separated by commas or new lines to get the net dB and the linear factors.
6. 6Press Copy on any result, and use the reference table to double-check common values. Everything runs locally.

About this tool

Decibel Converter turns decibels into the linear quantities they describe and back again, and it keeps the one distinction that trips almost everyone up front and center: whether you are working with a power quantity or an amplitude quantity. A decibel is a logarithmic ratio, but the formula depends on what is being measured. Power, intensity, and energy use dB = 10 x log10(P / P_ref), while amplitude quantities like voltage, current, and sound pressure use dB = 20 x log10(A / A_ref). The factor of two is not arbitrary: power is proportional to the square of an amplitude, so doubling a voltage is about +6 dB while doubling power is about +3 dB, and mixing the two formulas is the most common decibel mistake. This tool exposes both forms explicitly with a single toggle, so you always know which one you are using. It covers five jobs. Ratio to dB takes a plain linear ratio (output divided by input) and reports the decibel value for both the power and amplitude interpretations. dB to ratio goes the other way, turning a decibel figure into a linear factor and a percentage, which is handy for reading a filter response or an attenuation spec. The dBm tab converts between dBm and watts or milliwatts: dBm is power referenced to one milliwatt, the everyday unit of RF and wireless link budgets, where 0 dBm is exactly 1 mW and +30 dBm is 1 watt. The dBW tab does the same against a one-watt reference, and the tool always shows the dBm and dBW equivalents side by side so the 30 dB offset between them is never a surprise. The combine tab adds a list of gain and loss stages, because decibels add along a signal chain while the underlying linear gains multiply, and it reports the net dB along with the equivalent linear power and amplitude factors. A reference panel lists the values worth memorizing (3 dB is roughly double the power, 6 dB roughly double the amplitude, 10 dB exactly ten times the power, 20 dB ten times the amplitude) so you can sanity-check any result at a glance. This is the converter for audio engineers setting levels, RF and wireless engineers working link budgets in dBm, students learning the 10-log and 20-log rules, and anyone who needs to translate a gain spec into a real multiplier. Every calculation uses the browser's own math; nothing you enter is uploaded.

Free to use. Works in your browser. No signup, no login.