Engineering
Electrical Power Calculator
Calculate watts, equivalent resistance, energy use, and energy cost from voltage, current, operating time, and tariff. The circuit visual connects source voltage, load current, power, and accumulated energy without implying a universal AC model.
Electrical power (W)-
Equivalent resistance (ohms)-
Energy use (kWh)-
Energy cost-
Decision view
Source, load, power, and energy circuit
Source, load, power, and energy circuitVoltage and current establish the modeled operating point before time accumulates power into energy and cost.
Exact scenario comparisonCurrent (A) changes while all other entered assumptions remain constant.
| Current (A) | Electrical power (W) | Equivalent resistance (ohms) | Energy use (kWh) | Energy cost |
|---|
How to use Electrical Power Calculator
- Identify DC, single-phase AC, or three-phase AC before selecting a formula.
- Use true RMS measurements and real power for nonresistive AC loads.
- Confirm conductor, protection, thermal, and safety requirements with applicable standards.
Calculator guide
Understanding Electrical Power Calculator
For a DC load—or an AC load treated as unity power factor—power equals voltage times current. Real AC systems may require phase, power factor, waveform, and efficiency information.
Calculation method
How the calculation works
Apply DC or unity-power-factor relationships to calculate power and resistance, then multiply by time for energy and cost. Multiply volts by amperes for watts, divide voltage by current for equivalent ohms, multiply watts by hours and divide by 1,000 for kWh, then multiply by the entered energy rate.
Formula boundary
Know when V × I is not real AC power
Voltage and current magnitude alone can overstate useful power.
Worked situations
Practical examples
- 230 V at 8 A gives 1,840 W under the stated model.
- Across six hours, energy use is 11.04 kWh.
- At $0.18/kWh, the energy-only cost is $1.99.
Better inputs
Useful tips
- Measure standby and cycling loads over representative time.
- Use a power meter when power factor or harmonics are unknown.
- Separate energy charges from demand, fixed, tax, and time-of-use charges.
Before relying on the result
Limitations and common mistakes
- The formula assumes DC or unity-power-factor single-path power.
- AC power factor, phase configuration, harmonics, efficiency, reactive power, surge, and duty cycle are excluded.
- The page is not an electrical design or safety tool.
Reference
Key terms
- Voltage
- Electrical potential difference in volts.
- Current
- Rate of charge flow in amperes.
- Real power
- Rate of useful electrical energy transfer in watts.
- Energy
- Power accumulated over time, displayed in kWh.
Important note
Calculated from the entered values using the displayed engineering relationship. Confirm design values, load cases, safety factors, standards, and field conditions with a qualified professional.
Frequently asked questions
Does V × I always equal watts?
It does for DC and ideal unity-power-factor loads; AC real power can be lower.
Why is resistance calculated as V divided by I?
It is the equivalent resistance at the entered operating point under Ohm's-law assumptions.
Does cost include demand charges?
No. It multiplies energy by one entered per-kWh rate.
Can this size a breaker or wire?
No. Electrical design requires codes, load type, duty, temperature, installation, and protection rules.