Understanding your electricity usage is essential — whether you’re managing home appliances, solar panels, or an industrial setup. A kWh (kilowatt-hour) calculator helps you estimate energy consumption and cost accurately.
In this guide, we’ll explain what kWh means, how to calculate it, and include a free interactive kWh calculator you can use instantly.
Table of Contents
Use this tool to quickly find out how much energy a device uses and what it costs to run.
🔌 What Is a Kilowatt Hour (kWh)?
A kilowatt hour (kWh) is a measure of energy consumption. It represents the amount of energy used when a device that consumes 1 kilowatt (1,000 watts) of power runs for 1 hour.
1 kWh = 1,000 watts × 1 hour
For example:
- A 100W light bulb running for 10 hours uses
100 watts × 10 hours = 1,000 watt-hours = 1 kWh
⚙️ The kWh Formula
To calculate energy use in kilowatt-hours:
kWh = (Wattage × Hours of Use) / 1,000Example 1 — Home Appliance:
A 1500W space heater runs for 3 hours:
kWh = (1500 × 3) / 1000 = 4.5 kWhExample 2 — Solar Panel Output:
A 200W solar panel runs at full power for 5 hours:
kWh = (200 × 5) / 1000 = 1 kWh💡 Common Appliance kWh Examples
| Appliance | Power (Watts) | Usage (Hours) | Energy Used (kWh) |
|---|---|---|---|
| Laptop | 60W | 8h | 0.48 kWh |
| Refrigerator | 150W | 24h | 3.6 kWh |
| Air Conditioner | 1,500W | 8h | 12 kWh |
| Electric Oven | 2,000W | 2h | 4 kWh |
| LED Light Bulb | 10W | 10h | 0.1 kWh |
💲 How to Calculate Electricity Cost
Once you know your energy usage in kWh, you can estimate your bill:
Cost = kWh × Electricity RateIf your rate is $0.15 per kWh:
- A 4.5 kWh heater session costs:
4.5 × 0.15 = $0.68
🔋 Factors That Affect Your kWh Usage
- Device efficiency – Modern appliances use less power.
- Operating time – The longer something runs, the more kWh it consumes.
- Voltage and load – Some devices draw more current when overloaded.
- Standby power – Even idle electronics use small amounts of energy.
- Energy-saving modes – Smart devices throttle usage to reduce kWh draw.
🌞 Using kWh for Solar & Battery Sizing
If you’re designing a solar system or battery backup, kWh is the unit you’ll use to size everything:
- Solar output: Panel wattage × sunlight hours ÷ 1,000 = daily kWh
- Battery capacity: A 5 kWh battery can power 1 kW of load for 5 hours
Understanding kWh helps you match your panels, batteries, and usage precisely.
🧾 Summary
| Term | Meaning |
|---|---|
| Watt (W) | Instant power consumption |
| Kilowatt (kW) | 1,000 watts |
| kWh | Energy usage over time |
| Cost ($) | kWh × rate per kWh |
Formula Recap:
kWh = (W × Hours) / 1000
Cost = kWh × Rate