Watt Hours to Amp Hours Calculator
Convert battery energy between watt-hours and amp-hours in either direction by entering the energy value and the nominal DC voltage.
Result
10 Ah
120 Wh at 12 V is about 10 Ah
Quick Answer
To convert watt-hours to amp-hours, divide the watt-hours by the voltage: amp-hours = watt-hours divided by volts. For example, 120 Wh at 12 V equals 10 Ah. To reverse the conversion, multiply amp-hours by voltage to get watt-hours. Voltage is required for both directions because amp-hours alone carry no energy information without it.
What A Watt-Hours-to-Amp-Hours Calculator Measures
A watt-hours-to-amp-hours calculator converts between two battery capacity units that measure the same stored energy from different angles. Watt-hours (Wh) state the total energy a battery holds, combining both current and voltage into one number. Amp-hours (Ah) state only the charge capacity, which depends on voltage to become meaningful as an energy figure. The two units are linked by a single formula, and this calculator runs it in either direction using the DC nominal voltage you supply. Battery data sheets, solar chargers, inverters, and power banks all mix these two units freely. Knowing how to move between them lets you size a battery bank, compare two packs quoted in different units, or verify that a charger rating matches the battery it will serve. The result is always a DC figure; this tool does not apply an AC power-factor correction because amp-hour ratings are defined at DC.
How Watt-Hours to Amp-Hours Conversion Is Calculated
Wh to Ah: Ah = Wh ÷ V. Ah to Wh: Wh = Ah × V. V is the nominal DC voltage of the battery pack (for example 12 V, 24 V, or 48 V).
- Wh to Ah: Ah = Wh ÷ V.
- Ah to Wh: Wh = Ah × V.
- Ah = amp-hours, Wh = watt-hours, V = nominal DC voltage.
- DC formula only; no AC power factor is applied.
Using The Watt-Hours to Amp-Hours Calculator: Steps
Inputs
- Select Wh to Ah, or Ah to Wh from the dropdown.
- Energy value in Wh or capacity in Ah depending on chosen direction.
- Nominal DC voltage of the battery system (e.g. 12 V, 24 V, 48 V).
Steps
- Select the conversion direction from the dropdown.
- Enter the energy value in the first field (Wh or Ah, matching direction).
- Enter the nominal voltage in the voltage field.
- Read the converted result in the output field.
- To reverse the direction, change the dropdown and update the inputs.
Watt-Hours to Amp-Hours Example With Every Step Shown
120 Wh, 12 V, direction = Wh to Ah
- Apply formula: Ah = Wh ÷ V.
- Substitute values: Ah = 120 ÷ 12.
- Calculate: Ah = 10.
10 Ah (exact). Reverse check: 10 Ah × 12 V = 120 Wh.
Where This Wh-Ah Calculator Is Most Useful
Use this calculator when sizing a battery bank for a solar system, an RV, or a marine setup where the charger is rated in Wh and the battery is labelled in Ah. It also helps when comparing two battery packs quoted in different units, or when a power-bank specification lists mAh and you need the Wh equivalent for airline carry-on limits (divide mAh by 1,000 first to get Ah, then multiply by voltage).
For other engineering calculations, visit the engineering calculators hub, and check the glossary for definitions of common technical terms.
Assumptions
- The voltage entered is the nominal DC voltage of the battery system, not the fully charged or cut-off voltage.
- The formula is DC only; no power-factor correction is applied.
- Results assume the full rated capacity is available; real-world usable capacity depends on depth of discharge and temperature.
- Rounding to two decimal places where the result is not a whole number.
Limitations
- Does not account for battery efficiency losses or internal resistance.
- Does not apply AC power factor; use this for DC battery systems only.
- Nominal voltage varies across charge state; the result is an approximation at any voltage other than the true average discharge voltage.
- Does not cover multi-cell string calculations or series-parallel battery banks.
In Practice
The most common mistake is entering the rated voltage of a single cell instead of the full battery pack voltage. A 12 V lead-acid battery is made of six 2 V cells, and a 48 V lithium pack contains cells in series. Always use the voltage of the complete pack, not one cell, or the conversion will be off by the number of cells in series. Check the battery label or data sheet for the nominal system voltage before running the calculation.
Related Calculators
Watts to Amps Calculator
Convert watts and amps for DC, single-phase AC, and three-phase AC circuits using voltage and, where needed, power factor.
Open the CalculatorGear Ratio Speed Calculator
Find output RPM from a gear ratio or estimate vehicle road speed from engine RPM, tyre diameter, transmission ratio, and final drive.
Open the CalculatorBattery Runtime Calculator
Estimate how many hours a battery will run a given load. Enter capacity in Wh or Ah, voltage, system efficiency, and load in watts to find your runtime.
Open the CalculatorRelated Guides
- How To Calculate Conduit Size
Learn how to calculate the correct electrical conduit size using the National Electrical Code (NEC) 40% wire fill percentage rules and conductor area.
- How to Calculate Cycles Per Instruction (CPI Guide)
Understand CPI and IPC in computer architecture. Learn the CPI formula, how to find execution time from instruction count, and a worked example.
- How to Calculate Speed from Gear Ratio: Step-by-Step Guide
Learn how to calculate output speed from a gear ratio using teeth counts and input RPM. Two worked examples show reduction and overdrive gearing.
- How to Calculate Friction Loss in Pipe: Step-by-Step Guide
Calculate friction head loss in a water pipe using the Hazen-Williams equation. See the formula, C-coefficient values, and a worked example.
- How to Calculate GPM of a Pump: Flow Rate Made Simple
Learn how to calculate GPM flow rate using volume and time. Covers the basic formula, a bucket-test method, and worked examples with full steps.
- How To Calculate Mini Split Sizing
Learn how to calculate the correct mini split size for your room. Walk through a scenario covering square footage, ceilings, and insulation BTU adjustments.
Watt Hours to Amp Hours Calculator: Common Questions
What Is the Difference Between Wh and Ah in a Battery?
Watt-hours measure the total energy a battery can deliver, while amp-hours measure only the charge capacity at a given voltage. A 100 Ah battery at 12 V holds 1,200 Wh, while a 100 Ah battery at 48 V holds 4,800 Wh. The same Ah rating represents four times the energy at four times the voltage, which is why voltage must always accompany an Ah figure.
Can I Convert mAh to Wh With This Calculator?
Yes, with one extra step. Divide the milliamp-hours by 1,000 to get amp-hours first, then enter that Ah figure along with the voltage. For example, a 20,000 mAh power bank at 3.7 V becomes 20 Ah × 3.7 V = 74 Wh. Airlines set the carry-on limit at 100 Wh, so this conversion is useful for checking compliance.
Does Voltage Affect the Amp-Hour Rating of a Battery?
The amp-hour rating itself does not change with voltage, but the energy it represents does. Ah states how many amps the battery can supply for how many hours; watt-hours fold in the voltage to give actual energy. If you run the same load from a 12 V and a 24 V battery of identical Ah, the 24 V battery delivers twice the power per hour and lasts the same number of hours, supplying double the total energy.
Why Does This Calculator Only Handle DC Conversions?
Amp-hour ratings are a DC capacity unit defined by charge flow over time, and the Wh-to-Ah formula (Ah = Wh ÷ V) assumes a constant DC voltage. AC systems involve power factor and RMS voltage, which require separate calculations. For AC energy calculations, use a watts-to-kilowatt-hours approach rather than an amp-hour conversion.
How Accurate Is the Wh-to-Ah Result?
The calculation is exact for the nominal voltage you enter. Real-world accuracy depends on how closely that nominal voltage matches the battery's true average discharge voltage, which varies with charge state, temperature, and load. For most sizing purposes, nominal voltage gives a close enough result. For precision discharge modelling, use the battery manufacturer's actual discharge curve.
Sources
Last updated: . Reviewed for accuracy against the formula shown above.