Power, Energy & Cost Calculator
Estimate electrical power consumed (W), energy used (kWh), and operating cost over time.
What does “power consumed” mean?
Power consumed is the rate at which an electrical device uses energy. It is usually measured in watts (W) or kilowatts (kW). If you run a 100 W device, it consumes energy faster than a 10 W device. Your utility bill, however, is typically based on energy, not just power.
Energy is measured in kilowatt-hours (kWh). One kWh means using 1,000 watts for one hour. This calculator helps you move from raw electrical inputs to practical answers:
- Instantaneous power draw (W and kW)
- Daily and period energy consumption (kWh)
- Estimated electricity cost
Core formulas used in this calculator
Power (W) = Voltage (V) × Current (A)
Energy (kWh) = Power (W) × Time (hours) ÷ 1000
Cost = Energy (kWh) × Rate ($/kWh)
If you already know a device’s wattage from its label, you can use that directly. If not, voltage and current give you a quick estimate of power.
How to use the power consumed calculator
Method 1: Voltage and current
- Select Use Voltage (V) and Current (A).
- Enter voltage and current values.
- Enter hours used per day, number of days, and electricity rate.
- Click Calculate to view power, energy, and cost.
Method 2: Device wattage
- Select Use Device Wattage (W).
- Enter the appliance’s wattage from its label or manual.
- Provide usage hours, days, and tariff rate.
- Click Calculate.
Quick unit guide
| Term | Meaning | Typical Use |
|---|---|---|
| Watt (W) | Rate of power use | Device load right now |
| Kilowatt (kW) | 1000 watts | Larger loads, system-level planning |
| Kilowatt-hour (kWh) | Energy consumed over time | Utility billing |
| $/kWh | Price of one kilowatt-hour | Cost estimation |
Example calculation
Suppose a device runs at 230 V and 1.5 A for 4 hours/day over 30 days, with electricity priced at $0.16/kWh.
- Power = 230 × 1.5 = 345 W
- Daily energy = 345 × 4 ÷ 1000 = 1.38 kWh/day
- 30-day energy = 1.38 × 30 = 41.4 kWh
- Cost = 41.4 × 0.16 = $6.62 (approx.)
Why real-world values may differ
Calculated values are useful estimates, but your meter readings can vary due to:
- Duty cycle: many devices switch on and off instead of running continuously.
- Power factor: important for AC loads like motors and some electronics.
- Standby consumption: appliances may draw power even when “off.”
- Variable tariffs: time-of-use plans can change cost by hour.
Tips to reduce electricity consumption
- Use high-efficiency appliances (look for energy ratings).
- Turn off idle devices and chargers at the socket.
- Replace old lighting with LED bulbs.
- Use timers/smart plugs for predictable loads.
- Track major appliances monthly to spot unusual increases.
Frequently asked questions
Is power the same as energy?
No. Power is the rate of use (W), while energy is total use over time (kWh).
Can I calculate bill amount exactly?
This tool provides a close estimate. Exact bills can include taxes, fixed charges, and time-based pricing.
What if I only know wattage?
Use wattage mode. You do not need voltage and current when rated power is already known.