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Capacitance calculator

A-level Electricity

Capacitance is the charge stored on a capacitor per volt of potential difference.

C = Q / V

This free calculator is for 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

2.00 × 10−5 F

Working

  1. Write the equation
    C = Q / V
  2. Substitute the values
    C = (4 × 10−4) ÷ 20
  3. Calculate
    C = 2 × 10−5 F
  4. Give the answer to 3 significant figures
    C = 2.00 × 10−5 F

Worked example

Find C, the capacitance. Given: charge Q = 4.00 × 10⁻⁴ C; potential difference V = 20.0 V.

  1. Write the equation
    C = Q / V
  2. Substitute the values
    C = (4 × 10−4) ÷ 20
  3. Calculate
    C = 2 × 10−5 F
  4. Give the answer to 3 significant figures
    C = 2.00 × 10−5 F

Symbols and units

SymbolQuantitySI unit
CCapacitanceF
QChargeC
VPotential differenceV

Capacitance: rearranged

  • To find capacitance: C = Q / V
  • To find charge: Q = C V
  • To find potential difference: V = Q / C

Exam tip

Use the unit selector for μF and nF. 1 μF is 10⁻⁶ F.

Common questions

What is the formula for capacitance?

The equation is C = Q / V, where C is the capacitance (F); Q is the charge (C); V is the potential difference (V).

What units should I use for capacitance?

In SI units: capacitance in F, charge in C, potential difference in V. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange C = Q / V?

Rearranging gives these forms: to find capacitance: C = Q / V. to find charge: Q = C V. to find potential difference: V = Q / C.

Practise capacitance 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 Capacitance formula page. More electricity equations: Charge, current and time, Ohm’s law, Electrical power, Electrical power, Energy transferred, Resistors in series, Resistors in parallel, Resistivity. See the full list on the a-level physics equation calculator page.