What is electrical power and how is it calculated?

Electrical power is the rate at which electrical energy is transferred. On this page, electrical power is P = V × I. Mechanical power is force in newtons times velocity in meters per second. The switch converts a power entry between watts and mechanical horsepower. It does not compute P = I²R.

What's the difference between watts and volts?

Watts measure power (energy per unit time), while volts measure electrical potential difference. Power (watts) = Voltage (volts) × Current (amperes).

How do I calculate power from voltage and current?

Multiply voltage by current: P = V × I. For example, if you have 12 volts and 2 amperes, the power is 12 × 2 = 24 watts.

Why is power calculation important in electrical engineering?

Power calculations are essential for designing electrical systems, determining component ratings, calculating energy consumption, and ensuring electrical safety in circuits and devices.

Power Calculator

Calculate power, voltage, current, resistance, energy, or time. Enter the two known values. Uses standard formulas for DC and AC circuits.

Power unit

Calculation Type *

Voltage (V) *

Current (I) *

Smart Tips

• Power = Voltage × Current (P = V × I) for DC circuits

• Watts measure power, while watt-hours measure energy consumption over time

• Electrical resistance causes energy loss as heat in circuits

• Always ensure your power supply can handle the total wattage of connected devices

• This page uses P = V × I. It does not apply a power factor.

• Power in watts can be converted to kilowatt-hours for energy billing

Power Formulas

Type	Formula
Electrical Power	P = V × I
Mechanical Power	P = F × v
Voltage	V = P ÷ I
Current	I = P ÷ V
Resistance	R = V² ÷ P
Energy	E = P × t
Time	t = E ÷ P

Power Conversion Reference

Unit	Conversion
Watt (W)	1 W = 0.001 kW = 0.000001 MW
Kilowatt (kW)	1 kW = 1,000 W = 0.001 MW
Megawatt (MW)	1 MW = 1,000,000 W = 1,000 kW
Horsepower (hp)	1 hp = 745.6998715822702 W (mechanical horsepower)
BTU per Hour	This page does not convert BTU/h.

Key Insights

Power Formula

This page uses P = V × I. It does not multiply by a power factor.

Unit Conversions

The switch converts a typed power between watts and mechanical horsepower. It does not convert BTU per hour.

Electrical Safety

Understanding power consumption helps prevent circuit overloads and ensures electrical safety in your home or workplace.

Energy Efficiency

Calculate power consumption to optimize energy usage and reduce electricity costs over time.

Frequently Asked Questions

Electrical power is the rate at which electrical energy is transferred per unit time, measured in watts (W). This page calculates electrical power as P = V × I. It does not calculate P = I²R. From Ohm's law (V = IR), you can also use P = V²/R when you have voltage and resistance. These formulas are fundamental in circuit design and energy billing.

Watts (W) measure power—the rate at which energy is used or delivered (energy per second). Volts (V) measure voltage—the electrical potential difference that pushes current through a circuit. Amperes (A) measure current. The relationship is Power = Voltage × Current (P = VI), so one watt equals one volt times one ampere. For example, a 120 V outlet supplying 5 A delivers 600 W of power.

Multiply voltage by current: P = V × I. For example, 12 volts and 2 amperes give 12 × 2 = 24 watts. Make sure units are consistent (volts and amperes). For AC circuits with resistive loads the same formula applies to effective (RMS) voltage and current; for inductive or capacitive loads, power factor reduces the real power (watts) compared to the apparent power (volt-amperes).

Using Ohm's law (V = I × R), power can be written as P = V²/R when you know voltage and resistance, or P = I²R when you know current and resistance. Substitute V = IR into P = VI to get P = I²R, or I = V/R to get P = V²/R. These forms are useful when you have a resistor value and one of voltage or current, and they show that power dissipated in a resistor increases with the square of voltage or current.

Power calculations are used to size wires and fuses, choose components that can handle the load (e.g., resistors by wattage rating), estimate energy use (watts × time = energy in watt-hours or kilowatt-hours), and avoid overloads that cause overheating or fire. In renewable energy and batteries, power (kW) and energy (kWh) together determine how long a system can run. Accurate power math is central to safe and efficient electrical design.

Implemented formulas: P = VI, P = Fv, V = P/I, I = P/V, R = V²/P, E = Pt, and t = E/P. Force stays in newtons and velocity in m/s. Power inputs and power results use watts or mechanical horsepower, 745.6998715822702 W. A metric power result of at least 1,000 W is shown in kW. Energy stays in joules and time in seconds. Source: NIST SI units: https://physics.nist.gov/cuu/Units/units.html.

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Power

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Note: Power calculations are based on standard physics formulas. Actual power consumption may vary. Always consult equipment specifications for accurate power requirements.