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Electrical power (P = VI) calculator

GCSEA-level Electricity

The power transferred by an electrical component from the potential difference across it and the current through it.

P = V I

This free calculator is for GCSE and A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.

Quantity to find

1840 W

Working

  1. Write the equation
    P = V I
  2. Substitute the values
    P = 230 × 8
  3. Calculate
    P = 1840 W
  4. Give the answer to 3 significant figures
    P = 1840 W

Worked example

Find P, the power. Given: potential difference V = 230 V; current I = 8.00 A.

  1. Write the equation
    P = V I
  2. Substitute the values
    P = 230 × 8
  3. Calculate
    P = 1840 W
  4. Give the answer to 3 significant figures
    P = 1840 W

Symbols and units

SymbolQuantitySI unit
PPowerW
VPotential differenceV
ICurrentA

Electrical power (P = VI): rearranged

  • To find power: P = V I
  • To find potential difference: V = P / I
  • To find current: I = P / V

Exam tip

This works for any component, not only resistors.

Common questions

What is the formula for electrical power?

The equation is P = V I, where P is the power (W); V is the potential difference (V); I is the current (A).

What units should I use for electrical power?

In SI units: power in W, potential difference in V, current in A. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange P = V I?

Rearranging gives these forms: to find power: P = V I. to find potential difference: V = P / I. to find current: I = P / V.

Practise electrical power (p = vi) questions

Press the button for a question with random numbers. Work it out on paper first, then type your answer.

Related

Read the full explanation on the Electrical power formula page. More electricity equations: Charge, current and time, Ohm’s law, Electrical power, Energy transferred, Resistors in series, Resistors in parallel, Resistivity, EMF and internal resistance. See the full list on the physics equation calculator page.