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Charge, current and time calculator

GCSEA-level Electricity

Charge is the current multiplied by the time for which it flows.

Q = I t

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

75.0 C

Working

  1. Write the equation
    Q = I t
  2. Substitute the values
    Q = 2.5 × 30
  3. Calculate
    Q = 75 C
  4. Give the answer to 3 significant figures
    Q = 75.0 C

Worked example

Find Q, the charge. Given: current I = 2.50 A; time t = 30.0 s.

  1. Write the equation
    Q = I t
  2. Substitute the values
    Q = 2.5 × 30
  3. Calculate
    Q = 75 C
  4. Give the answer to 3 significant figures
    Q = 75.0 C

Symbols and units

SymbolQuantitySI unit
QChargeC
ICurrentA
tTimes

Charge, current and time: rearranged

  • To find charge: Q = I t
  • To find current: I = Q / t
  • To find time: t = Q / I

Exam tip

Time in seconds. A current in mA must be converted to A, or use the unit selector.

Common questions

What is the formula for charge, current and time?

The equation is Q = I t, where Q is the charge (C); I is the current (A); t is the time (s).

What units should I use for charge, current and time?

In SI units: charge in C, current in A, time in s. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange Q = I t?

Rearranging gives these forms: to find charge: Q = I t. to find current: I = Q / t. to find time: t = Q / I.

Practise charge, current and time 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 Electric charge formula page. More electricity equations: Ohm’s law, Electrical power, 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.