Watt-hour Calculator — mAh to Wh Converter & Energy Cost Calculator
Welcome to our watt-hour calculator, a versatile tool that lets you convert electric charge (mAh or Ah) to energy (Wh), calculate energy consumption from power and time, and optionally estimate electricity costs in multiple world currencies — including US Dollar ($), Russian Ruble (₽), Euro, and more.
What Is a Watt-Hour?
A watt-hour (Wh) is a unit of electrical energy equal to the energy transferred by one watt of power over one hour. It is widely used to rate battery capacity for laptops, phones, and electric vehicles, and to measure household electricity consumption (usually in kilowatt-hours, kWh).
- 1 Wh = 3,600 joules (J)
- 1 kWh = 1,000 Wh
- 1 mWh = 0.001 Wh
How to Use the Watt-hour Calculator
Mode 1 — mAh / Ah to Wh (Battery Capacity)
- Select Charge → Energy mode.
- Enter the battery charge in mAh (milliamp hours) or Ah (amp hours).
- Enter the battery voltage in volts (V).
- Click Calculate — you instantly get energy in Wh, kWh, mWh, joules, and kilojoules.
Mode 2 — Power × Time → Energy + Cost
- Select Power × Time mode.
- Enter the device power in W, kW, or mW.
- Enter the time the device runs in hours.
- Optionally enter the electricity price per kWh and choose your currency (USD, RUB, EUR, GBP, JPY, CNY, CAD, AUD, INR).
- Click Calculate.
How Does the mAh to Wh Converter Work?
Milliamp hours (mAh) measure electric charge — how much current a battery can supply over time. To find the energy stored, you also need the voltage:
Wh = Ah × V
Milliamp Hours to Watt-Hours — An Example
A lithium-ion polymer battery with 1,200 mAh and a nominal voltage of 3.7 V:
For reference, laptop batteries typically range from 22 Wh to nearly 100 Wh.
How to Calculate Watt-Hours from Power and Time
If you know a device's power rating and how long it runs:
kWh = Wh ÷ 1000
Example: a 100 W light bulb running for 8 hours consumes 800 Wh = 0.8 kWh.
Electricity Cost Calculation
Once you have the energy in kWh, multiply by your electricity tariff:
Our calculator supports 9 world currencies: USD ($), RUB (₽), EUR (€), GBP (£), JPY (¥), CNY (¥), CAD (C$), AUD (A$), INR (₹). The ruble is listed second after the dollar, reflecting its wide use by our audience.
Why Convert Amp Hours to Watt-Hours?
Amp-hours alone don't tell you how much energy a battery holds — two batteries with the same Ah rating but different voltages store different amounts of energy. Watt-hours give you a universal, voltage-independent measure of energy, making it easy to compare batteries of different chemistries (Li-ion 3.7 V vs. lead-acid 12 V) or estimate how long a battery will power a given device.
Metric and American Units
The calculator works natively in SI (metric) units: milliamp hours, amp hours, volts, watts, kilowatts, watt-hours, joules. For American engineering contexts, power can also be entered in milliwatts (mW) or kilowatts (kW), and energy results are shown in multiple unit conversions simultaneously.
FAQs
What is the difference between Wh and kWh?
1 kilowatt-hour (kWh) = 1,000 watt-hours (Wh). kWh is used on electricity bills; Wh is more practical for small batteries.
How do I find the Wh rating of a battery that shows only mAh?
Use the formula: Wh = mAh × V / 1000. You need to know the nominal voltage, usually printed on the battery label.
How many watt-hours does a typical phone battery have?
Most smartphones have batteries of 10–20 Wh (e.g., 3,000 mAh at 3.85 V ≈ 11.55 Wh).
Can I use this calculator for solar panels?
Yes — enter the panel's rated power (W) and the daily sunshine hours to find daily energy output (Wh). Then divide by 1,000 for kWh and multiply by your electricity price to estimate savings.