All Charge Units

How to Convert Electric Charge Units?

Electric charge is measured in Coulombs (SI unit) or ampere-hours (practical unit for batteries). One Coulomb equals the charge transported by one ampere of current in one second. Converting between Coulombs and ampere-hours requires the relationship: 1 Ah = 3600 C. Our converter handles both scientific prefixes (milli, micro, nano, pico) and practical battery units.

Frequently Asked Questions

What units of electric charge does this converter handle?

This converter handles the SI coulomb and its standard SI-prefixed forms (picocoulomb, nanocoulomb, microcoulomb, millicoulomb, coulomb, kilocoulomb), the ampere-hour family (mAh, Ah) widely used for batteries, and the elementary charge e for atomic physics contexts. The coulomb is the SI derived unit of electric charge, equal to one ampere times one second (1 C = 1 A*s). Since the 2019 SI redefinition, the coulomb is defined indirectly by fixing the elementary charge e at exactly 1.602176634 x 10^-19 C. The faraday (96485.33212... C/mol) is excluded as a chemistry-specific molar unit; if you need molar charge, multiply moles by the Faraday constant separately.

What is the exact conversion between coulombs and ampere-hours?

1 ampere-hour = exactly 3600 coulombs, because 1 A flowing for 3600 s deposits 1 A*s * 3600 = 3600 C of charge. So 1 mAh = 3.6 C exactly. A typical AA NiMH cell at 2500 mAh stores 2500 * 3.6 = 9000 C of charge. A phone battery at 4500 mAh holds 16,200 C. An electric-car battery at 100 kWh and 400 V averages 250 Ah = 900,000 C. The factor 3600 is exact because the SI second and the SI hour both have exact integer relations. Note that ampere-hours specify charge, not energy; energy in watt-hours equals ampere-hours times average voltage (in volts), and this distinction is the source of many battery-spec misreadings.

When should I use C, mAh, or e?

Use coulombs (C) and its prefixes for capacitor charge (a 1 uF capacitor at 5 V holds 5 uC), electrostatic experiments, electrochemistry (1 Faraday = 96485 C per mole of electrons), and physics problems involving current integrals. Use milliampere-hours (mAh) and ampere-hours (Ah) exclusively for battery capacity: this is the convention every smartphone, power bank, laptop, and EV spec sheet uses. Use the elementary charge e (1.602176634 x 10^-19 C) for atomic and particle physics, ion counts in mass spectrometry, and quantum-electronics contexts. Mixing C and Ah in one document is awkward; pick the audience-appropriate unit.

How precise are the conversions and what rounding is right?

Internally the tool uses 64-bit floating-point and exact definitional factors: 1 Ah = 3600 C exactly, 1 e = 1.602176634 x 10^-19 C exactly (post-2019). All conversions are decimal-exact apart from the floating-point display step, giving 15+ significant digits of internal precision. In practice, battery-capacity ratings are nominal +/-5% to +/-15% (real-world capacity depends on temperature, discharge rate, and age), so showing more than 3 significant figures for a battery is theatrical. For metrology and electrochemistry, 6 to 9 significant figures may matter; for physics involving the elementary charge, use as many digits of e as your problem requires.

What are the common gotchas with battery capacity?

Several. First, mAh measures charge, not energy: a 10000 mAh power bank at 3.7 V holds 37 Wh, but if it outputs 5 V via a boost converter the user-visible energy is the same 37 Wh (minus losses), so 'effective' 5 V mAh is roughly 10000 * 3.7/5 = 7400 mAh. Second, the C-rate: 'a 2 Ah cell at 1C' means 2 A draw; 'at 0.5C' means 1 A. Third, Peukert's effect: discharging faster delivers less total charge than the nameplate (lead-acid loses 30% at high C-rates). Fourth, depth-of-discharge: a battery's 'usable capacity' is often 80% of nominal for cycle-life reasons. The converter does pure unit arithmetic; battery physics adds nontrivial corrections.

What is the relationship between charge, current, and capacitance?

Three foundational electrostatic relations link these. (1) Q = I * t : charge equals current times time, with I in amperes, t in seconds, Q in coulombs. (2) Q = C * V : charge on a capacitor equals capacitance times voltage, with C in farads and V in volts. (3) E = 0.5 * C * V^2 = 0.5 * Q * V : energy stored in the capacitor's electric field, in joules. So 1 farad is enormous: a 1 F supercapacitor charged to 5 V holds 5 C = 1.39 mAh of charge and 12.5 J of energy. Lithium-ion batteries store ~250 J/cm^3, supercaps ~5 J/cm^3 - hence supercaps complement, not replace, batteries.

How is the coulomb defined in the modern SI system?

Since 2019, the coulomb is no longer the primary defined unit; instead, the SI fixes the elementary charge e at exactly 1.602176634 x 10^-19 C. The coulomb is therefore derived: 1 C = 1/(1.602176634 x 10^-19) elementary charges = approximately 6.241509074 x 10^18 e. Equivalently, since 1 A is defined by fixing e and the second, 1 C = 1 A*s automatically follows. Before 2019, the ampere was defined operationally via the force between two parallel wires (the 4*pi x 10^-7 H/m permeability of free space was exact). The 2019 redefinition replaced that with a constant-e definition, making the coulomb exactly counted in electrons rather than referenced to a mechanical force. The BIPM coordinates this redefinition globally.

What are edge cases at the atomic and macroscopic scales?

At the atomic scale: a single electron carries -1 e = -1.602176634 x 10^-19 C. A water molecule has zero net charge but a dipole moment of 6.18 x 10^-30 C*m. A protein with charge state +5 carries 5e = 8.01 x 10^-19 C. Mass spectrometry routinely counts individual elementary charges. At macroscopic scales: a lightning bolt transfers 15 to 350 C in microseconds (peak currents up to 200 kA). A car battery is roughly 50 Ah = 180,000 C. The earth-ionosphere capacitor holds about 500 kC. The converter handles 10^-19 C to 10^6 C without issue, but ensure your input is in coherent units; mixing e with C in the same calculation needs careful prefix tracking.

Units

Coulomb (C)

The SI unit of electric charge, named after Charles-Augustin de Coulomb. One Coulomb is the amount of charge transferred by a current of one ampere flowing for one second. It equals approximately 6.242 x 10^18 elementary charges (electrons or protons).

Milliampere-hour (mAh)

The most common unit for battery capacity in consumer electronics. Smartphones typically have 3000-5000 mAh batteries, while wireless earbuds may have 30-60 mAh. One mAh equals 3.6 Coulombs of charge.

Ampere-hour (Ah)

Used for larger batteries such as car batteries, power tools, and energy storage systems. A typical car battery has 40-100 Ah capacity. One Ah equals 1000 mAh or 3600 Coulombs.

Microcoulomb (uC)

Used in scientific measurements and electrostatics. Common in capacitor charge calculations, piezoelectric sensors, and laboratory experiments. One microcoulomb equals 0.000001 Coulombs.

Nanocoulomb (nC)

Used in precision electronics, semiconductor physics, and charge measurements in microchips. Essential for understanding charge transfer in transistors and integrated circuits.

Common Electric Charge Conversions