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Engineering Unit Converter

Convert voltage, current, power, energy, frequency, charge and more between units — including logarithmic dBm, dBW and dBV.

Converter Reference

Result in millivolt
1000 mV
Base unit
1 V 1 V in voltage

Notes

The value field understands engineering notation — “4k7”, “470n”, “1µ” all work. Decibel units (dBm, dBV) are referenced as labelled: dBm is relative to 1 mW, dBV to 1 V. Converting a non-positive power or voltage to decibels is undefined.

How Engineering Unit Converter works

Most engineering unit conversion is a single multiplication by a fixed factor, because SI units form a coherent system: watts are volts times amperes, joules are watts times seconds, coulombs are amperes times seconds. The metric prefixes are then just powers of ten, running from pico through nano, micro, milli, kilo, mega and beyond in steps of a thousand.

Logarithmic units break that pattern and are where mistakes concentrate. A decibel expresses a ratio, so a decibel value alone is meaningless — it needs a reference, which is what the suffix encodes. dBm is referenced to one milliwatt, dBW to one watt, and dBV to one volt.

The factor of 10 versus 20 in front of the logarithm is the other trap. Power ratios use 10 × log₁₀ because power is the quantity being compared directly; amplitude ratios — voltage, current, pressure — use 20 × log₁₀, because power goes as the square of amplitude and the square becomes a factor of two once inside the logarithm. Using the wrong one doubles or halves your answer in decibels.

A few useful anchors make decibel work quick mentally: 3 dB is a factor of two in power, 10 dB is a factor of ten, and 0 dBm is exactly one milliwatt. From there, 20 dBm is 100 mW and −30 dBm is one microwatt.

Reference

  • dBm = 10 × log₁₀(P / 1 mW); P(mW) = 10^(dBm / 10)
  • dBW = 10 × log₁₀(P / 1 W); dBW = dBm − 30
  • dBV = 20 × log₁₀(V / 1 V)
  • Power ratio in dB = 10 × log₁₀; amplitude ratio in dB = 20 × log₁₀
  • Energy: 1 Wh = 3600 J; 1 kWh = 3.6 MJ; 1 eV = 1.602 × 10⁻¹⁹ J
  • Charge: 1 mAh = 3.6 C; frequency: 1 Hz = 60 rpm

How to use this converter

  1. Choose a quantity

    Pick the physical quantity — voltage, current, power, energy, frequency, charge — to scope the unit list.

  2. Enter a value with its unit

    Type the number and select its unit. Metric prefixes are handled directly.

  3. Read every equivalent

    The value is shown in all compatible units at once, so you do not have to pick a target first.

  4. Mind the reference for decibels

    For logarithmic units, confirm you are using the right reference and the right 10-versus-20 factor.

Worked examples

A Wi-Fi transmit power

Given
20 dBm
Result
100 mW, or −10 dBW

0 dBm is 1 mW and every 10 dB is a factor of ten. dBW is always dBm minus 30.

Battery energy

Given
A 3000 mAh cell at 3.7 V nominal
Result
11.1 Wh, or 39,960 J

mAh is charge, not energy. Multiplying by voltage is what turns it into something comparable across chemistries.

The 10-versus-20 trap

Given
A voltage ratio of 2
Result
6.02 dB — not 3.01 dB

Amplitude ratios take 20 × log₁₀. Using the power formula on a voltage ratio halves your answer, a classic and easily missed error.

When to use it

  • Converting RF power between dBm, dBW, and milliwatts when reading a radio datasheet.
  • Turning a battery’s mAh rating into watt-hours to compare across voltages and chemistries.
  • Converting motor speed between rpm and hertz.
  • Moving between joules, watt-hours, and kilowatt-hours in energy calculations.
  • Applying metric prefixes correctly when a datasheet and a schematic use different scales.

Things to watch out for

  • A decibel figure without a reference is incomplete. dB alone expresses a ratio; dBm, dBW, and dBV are absolute because their reference is stated.
  • Use 10 × log₁₀ for power and 20 × log₁₀ for amplitude. Getting this backwards is the most common decibel error in practice.
  • mAh is charge, not energy. Comparing mAh figures across different voltages is meaningless — convert to watt-hours first.
  • Prefix case matters: M is mega and m is milli, a factor of a billion apart. Similarly K is kelvin while k is kilo.

Frequently asked questions

How do I convert dBm to watts?

Power in milliwatts is 10 raised to the dBm value divided by ten, then divide by 1,000 for watts. So 30 dBm is 1,000 mW, or 1 W. Working backwards, dBm is 10 × log₁₀ of the power in milliwatts.

When do I use 10 log versus 20 log?

Use 10 × log₁₀ when comparing powers, and 20 × log₁₀ when comparing amplitudes such as voltage or current. The factor of two appears because power is proportional to amplitude squared, and squaring inside a logarithm becomes multiplication outside it.

What is the difference between dBm and dBW?

Only the reference. dBm is referenced to one milliwatt and dBW to one watt, so dBW = dBm − 30. RF and communications work overwhelmingly uses dBm because typical powers are small.

How do I convert mAh to watt-hours?

Multiply the amp-hours by the nominal voltage. A 3000 mAh cell at 3.7 V holds 3.0 × 3.7 = 11.1 Wh. This conversion is essential when comparing cells of different chemistries, since mAh alone ignores voltage entirely.

What is 0 dBm?

Exactly one milliwatt. It is a fixed absolute power, not a zero-power condition — a common misreading. Negative dBm values are perfectly normal and simply mean less than a milliwatt.

Why does 3 dB keep appearing?

Because 3.01 dB is a factor of two in power, and half power is where a filter’s cutoff is conventionally defined. Ten decibels is a factor of ten, which is the other anchor worth memorising for quick mental work.

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