Q = CV Engineering Calculator

Calculator

Select which variable to solve, enter the other values, choose units, and calculate.

Solve for

Charge value

Charge input unit

Capacitance value

Capacitance input unit

Voltage value

Voltage input unit

Charge result unit

Capacitance result unit

Voltage result unit

Calculation History

Time	Mode	Inputs	Result
No calculations stored yet.

Plotly Graph

The graph plots charge against voltage using the effective capacitance from your calculation.

Example Data Table

Case	Capacitance	Voltage	Charge	Energy
Sensor hold stage	10 µF	5 V	50 µC	0.000125 J
Filtering node	22 µF	12 V	264 µC	0.001584 J
Pulse network	47 nF	250 V	11.75 µC	0.001469 J
HV lab sample	100 pF	2 kV	200 nC	0.0002 J

Formula Used

The base capacitor relation is Q = C × V, where charge is in coulombs, capacitance is in farads, and voltage is in volts. Rearranging gives C = Q ÷ V and V = Q ÷ C. The page converts every entry into base SI units before solving.

After finding the unknown, the calculator also reports stored energy using E = 1/2 × C × V². This extra value helps with capacitor selection, charge storage checks, and comparison work during engineering analysis, lab review, and design validation.

How to Use This Calculator

Choose whether you want to solve for charge, capacitance, or voltage.
Enter the two known values and select the correct engineering units.
Pick the display units for each result field.
Press Calculate to show the result above the form.
Review the derived values, graph, and saved history rows.
Use the CSV or PDF buttons when you need a downloadable report.

FAQs

1) What does Q = CV mean?

Q = C × V states that stored electric charge equals capacitance multiplied by applied voltage. Use it for capacitor sizing, circuit checks, and quick unit-based engineering calculations.

2) Which units work here?

Common units include coulombs, millicoulombs, microcoulombs, farads, microfarads, nanofarads, picofarads, volts, millivolts, and kilovolts. The calculator converts them before solving.

3) Can I solve for capacitance or voltage too?

Yes. Change the solve option to capacitance or voltage. Enter the other two variables, and the calculator rearranges the equation automatically.

4) Why can capacitance come out negative?

A negative result usually means charge and voltage signs oppose each other. That can happen in signed calculations, but passive physical capacitance is normally treated as positive.

5) Why is stored energy included?

Energy helps engineers judge stored electrical potential. The page computes E = 1/2CV² after each valid solution, using the effective capacitance and voltage.

6) Does the graph change after every calculation?

Yes. The Plotly chart updates after calculation and plots charge against voltage using the solved or supplied capacitance. That makes trends easy to inspect.

7) What causes division errors?

Trying to solve capacitance with zero voltage, or voltage with zero capacitance, causes division by zero. Enter nonzero denominators for those modes.

8) Can I export my results?

Yes. Use the CSV button for history rows and the PDF button for a printable report. Both export the current on-page calculation details.