Watt Converter Calculator

Related Calculators

Real power (W): The part of electrical power that does useful work, measured in watts. In AC circuits, real power is lower than apparent power when power factor is less than 1.[1][3]

Apparent power (VA): Volts times amps in an AC circuit using RMS values. It matches watts only when power factor equals 1.[1][3]

Power factor (PF): A number that links real power and apparent power in AC circuits. For most basic load calculations here, it should be greater than 0 and usually up to 1.[1]

Voltage (V): The electrical push that moves charge through a circuit.

Current (A): The flow of electric charge through a wire or device.

Energy (kWh): Power used over time. One kilowatt-hour means using 1000 watts for 1 hour.

Three-phase voltage type: In three-phase systems, line-to-line voltage is measured between two lines, while line-to-neutral voltage is measured from one line to neutral.[1]

Mistake: Using Real power (W) when your device label actually shows VA.
Fix: In Advanced options, change If you are entering power, what kind is it? to apparent power and fill in Apparent power (VA).

Mistake: Leaving Power factor (PF) blank for an AC single-phase or AC three-phase calculation.
Fix: Enter Power factor (PF) for AC modes. If the load is purely resistive, use 1.

Mistake: Entering 0 for Voltage (V) when solving for Current (A), or 0 for Current (A) when solving for Voltage (V).
Fix: Use a non-zero Voltage (V) or Current (A), because the calculator cannot divide by zero.

Mistake: Picking AC three-phase but using the wrong Three-phase voltage type.
Fix: Match Three-phase voltage type to how the voltage was measured: line-to-line between two lines, or line-to-neutral from one line to neutral.

Mistake: Confusing Time with Time unit in energy problems.
Fix: Enter the number in Time, then choose the right Time unit so Energy (kWh) and Time (hours) are converted correctly.

Mistake: Thinking a larger Apparent power (VA) than Real power (W) means the answer is wrong.
Fix: Check Power factor (PF). When PF is below 1, Apparent power (VA) is expected to be higher than Real power (W).

• This calculator uses standard balanced-circuit formulas for DC, single-phase AC, and three-phase AC. Real systems can differ if the load is unbalanced or the waveform is not close to normal RMS conditions.
• For AC results, Power factor (PF) must be entered correctly when it affects the formula. A wrong PF changes watts, amps, and VA directly.
• In DC mode, PF is treated as 1 internally and hidden AC-only inputs should not affect the result.
• Three-phase results depend on choosing the correct Three-phase voltage type. Using line-to-line when your voltage is line-to-neutral, or the reverse, will give the wrong answer.
• Energy conversions assume constant power over the whole Time period. If power changes during use, actual Energy (kWh) can be different.
• The calculator allows negative real power or current if entered, which can represent reverse power flow or a different sign convention. That is unusual for most household loads.
• Results are blocked when a required visible input is missing, not numeric, or would cause division by zero, such as zero Voltage (V), zero Current (A), zero Time, or PF less than or equal to 0 in divide-by-PF calculations.

Core equations

The calculator follows the selected mode and system type, then solves the matching electrical relationship. For DC, power factor is treated as 1. For AC, real power, apparent power, and power factor are kept separate so watts and VA are not mixed up.[1][3]

P = V x I x PF

I = P / (V x PF)

V = P / (I x PF)

P_3phase_line-to-line = sqrt(3) x V_LL x I x PF

P_3phase_line-to-neutral = 3 x V_LN x I x PF

S = P / PF

Energy(kWh) = (Power(W) / 1000) x Time(hours)

Power(W) = (Energy(kWh) x 1000) / Time(hours)

How the calculator decides what to use

If you solve for Power (watts), Current (amps), or Voltage (volts), the calculator uses the electrical formula for the chosen System type. In AC modes, Power factor (PF) is required when it changes the answer. In AC three-phase mode, the Three-phase voltage type decides whether the calculator uses the sqrt(3) x V_LL form or the 3 x V_LN form.[1]

If you choose Apparent power (VA) in Advanced options, the calculator first interprets that value as S, then converts to real power with power factor before solving for the requested quantity. This prevents the common mistake of treating VA and W as the same thing when PF is below 1.[1][3]

Time conversion

For energy math, Time is converted to hours first. Minutes are divided by 60, and days are multiplied by 24. Then the energy or power formula is applied.

Mini example

Example:

AC single-phase, solve for Current (A), with Voltage (V) = 120, Real power (W) = 1500, and Power factor (PF) = 0.8.

I = 1500 / (120 x 0.8) = 15.625 A

S = 1500 / 0.8 = 1875 VA

So the Calculated value is 15.625 A, and Apparent power (VA) is 1875. Because PF is less than 1, VA is larger than W, which is expected.[1][3]

Assumptions used in results

The three-phase formulas assume a balanced system and RMS voltage/current values.[1] Negative real power is allowed and can represent reverse real power flow under a sign convention, which is one reason a negative result can appear in special cases.[2]

The calculator shows N/A or an error instead of forcing impossible math when a needed divisor is zero or missing, such as zero Voltage (V), zero Current (A), zero Time, or PF less than or equal to 0 in divide-by-PF cases.