Electric / Voltage Converter

This converter changes a quantity of electric charge from one unit into another. It supports the coulomb, the ampere-hour, the faraday, the abcoulomb and the statcoulomb, along with the sub-multiples microfaraday, millifaraday and picofaraday. Enter your value, choose the unit it is in and the unit you want, and read the result.

One point of clarification before anything else, because the page title is misleading: despite being listed as a voltage converter, the units this tool works with measure charge, not voltage. Charge is the amount of electricity; voltage is the potential difference that pushes it. If you need to convert volts to millivolts or kilovolts, those are simple decimal prefixes and this tool is not what you want.

What is electric charge?

Charge is a quantity of electricity — how much, rather than how fast or how hard. The SI unit is the coulomb (C), defined as the charge carried by a current of one ampere flowing for one second. So charge, current and time are locked together by a single relationship:

• Q = I × t — charge equals current multiplied by time

That equation is why the ampere-hour exists as a unit at all, and why battery capacities are quoted the way they are.

A worked example: battery capacity

A phone battery is rated 3,000 mAh. That is 3 ampere-hours. One ampere-hour is one amp for one hour, and an hour is 3,600 seconds, so:

• 3 Ah × 3,600 = 10,800 coulombs

Put another way, that battery can deliver 3 amps for one hour, or 300 milliamps for ten hours, or 1 amp for three hours — the charge is the same, only the rate changes. This is also why comparing two batteries on mAh alone is only fair if they run at the same voltage; energy is charge multiplied by voltage, and a 3,000 mAh cell at 3.7 V holds far more energy than the same figure at 1.2 V.

The units in the list

• Coulomb (C) — the SI unit. One amp-second.
• Ampere-hour (Ah) — 3,600 coulombs. The practical unit for batteries; milliamp-hours (mAh) are thousandths of it.
• Faraday — 96,485 coulombs, the charge carried by one mole of electrons. It is the working unit of electrochemistry, used for calculating how much material a given charge will deposit or dissolve in electroplating and electrolysis.
• Abcoulomb — 10 coulombs, from the electromagnetic CGS system.
• Statcoulomb — about 3.336 × 10^-10 coulombs, from the electrostatic CGS system. Also called the franklin or esu.

The microfaraday, millifaraday and picofaraday entries are decimal fractions of the faraday above. Be careful with these: they read almost identically to the microfarad, millifarad and picofarad, which are units of capacitance and a completely different quantity. Capacitance in farads and charge in faradays are unrelated despite both honouring Michael Faraday.

How to use the converter

1. Enter the charge value you have.
2. Select its unit from the first dropdown.
3. Select the unit you want in the second dropdown.
4. Read the converted figure and copy it.

Where this comes up

Battery and power-bank sizing, where datasheets mix mAh, Ah and occasionally coulombs. Electroplating and electrolysis calculations, where Faraday's laws relate charge directly to the mass of material deposited. Capacitor discharge work, where the charge stored tells you how much energy is released. Physics coursework, where problems are often set in CGS units and answered in SI. In each case the arithmetic is simple, and the risk is picking the wrong unit from a list where several names look alike.

A note on CGS units

Two of the entries, the abcoulomb and the statcoulomb, come from the centimetre-gram-second systems that preceded SI. They are not simply scaled versions of the coulomb in the way that the milliamp is a scaled amp: the electromagnetic and electrostatic CGS systems defined charge from different physical laws, which is why one is a clean factor of ten and the other is an awkward 3.336 × 10^-10. That second figure is tied to the speed of light, which is the fingerprint of the electrostatic system. You will only meet them in older literature, but when you do, converting them by hand is easy to get wrong.

Frequently asked questions

How many coulombs are in an ampere-hour?

3,600 — one amp flowing for 3,600 seconds. So 1,000 mAh is 3,600 coulombs.

Is a faraday the same as a farad?

No. A faraday is a quantity of charge, 96,485 coulombs. A farad is a unit of capacitance, one coulomb per volt. The similar names cause a great deal of confusion and the two are not convertible.

Can this tool convert volts?

No. Volts, millivolts and kilovolts differ only by powers of ten, so no lookup is needed — multiply or divide by a thousand.

How do I get energy from charge?

Multiply charge by voltage. A coulomb moved through one volt is one joule. That is why battery energy is properly quoted in watt-hours rather than amp-hours.

What are the abcoulomb and statcoulomb for?

They belong to the two older CGS unit systems and appear mainly in physics textbooks and historical papers. Modern work uses coulombs throughout.

Related tools

• Power Converter — watts, horsepower and BTU per hour.
• Time Unit Converter — charge is current multiplied by time, so the units meet here.
• Byte/Bit Converter — the other place decimal prefixes cause trouble.
• Percentage Calculator — for efficiency and capacity-loss figures.