Watt-hours measure energy. Battery packs, power banks and EV batteries are compared in Wh or kWh because amp-hours alone ignore voltage. Airlines limit power banks to 100 Wh in carry-on luggage.
How to use the Watt-Hour Calculator
- Calculate from
- Voltage
- Capacity
- Power
- Time
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Choose battery capacity or power × time and enter the values.
Inputs explained
| Field | What to enter |
|---|---|
| Calculate from | Choose one: Battery voltage and capacity, Power and time |
| Voltage | Units: V, mV, kV, µV, MV |
| Capacity | Units: mAh, Ah |
| Power | Units: W, kW, MW, hp, mW |
| Time | Units: h, min, days |
Example values
How the main result changes when Voltage changes and everything else stays at the example values above:
| Voltage (V) | Energy (Wh) |
|---|---|
| 1.85 | 37 |
| 2.78 | 55.5 |
| 3.7 | 74 |
| 4.63 | 92.5 |
| 5.55 | 111 |
| 7.4 | 148 |
Formula
Wh = V × Ah, Wh = P × t (h)
Worked example
Inputs — Calculate from: Battery voltage and capacity; Voltage: 3.7 V; Capacity: 20,000 mAh.
Results — Energy = 74 Wh; Airline carry-on (≤ 100 Wh) = Allowed.
Key terms
- Watt-hour
- Energy of one watt for one hour, 3,600 J.
Frequently asked questions
How many Wh is a 20,000 mAh power bank?
About 74 Wh at 3.7 V.
Why use Wh rather than mAh?
Wh includes voltage, so it measures true energy.
How do I convert Wh to kWh?
Divide by 1,000.
How long will a battery last?
Hours = Wh ÷ device power in W (minus conversion losses).