Example 1
C = 10 µF.
Capacitance calculator
Type charge Q [C] and voltage U [V]. The calculator computes C = Q/U: 1e-4 C at 10 V is 10 µF, and 2e-6 C at 5 V is 0.4 µF. Zero volts does not divide.
Energy: E = ½ C U². Series: 1/Cz.
Result
Charge Q (C) and Voltage U (V). The result shows up here.
How it works
Capacitance is charge over voltage: C = Q/U. At Q = 1e-4 C and U = 10 V you get 1e-5 F, or 10 µF. At 2e-6 C and 5 V you get 4e-7 F, or 0.4 µF. At 1 nC and 1 V you get 1 nF. 1 F at 1 V is 1 C; a typical electrolytic is microfarads.
The form has two fields: Q in coulombs and U in volts. The result is in farads, or µF and nF when C is small. 1 µF = 1e-6 F. 1e-4 is the easy entry for 0.0001 C. A comma, a period, and e notation mean the same Q.
U must not be zero, because you do not divide by zero. Typed 0 in U is rejected. Zero coulombs at nonzero U gives C = 0. Both fields need a number before 10 µF appears.
E = ½ C U² is on the neighbouring page and computes energy, not capacitance. Two C in series obey 1/Cz = 1/C1 + 1/C2. In parallel Cz = C1 + C2. Here one capacitor from Q and U.
C = ε0 A / d is a different problem: plate area and gap. This calculator does not know area. It already takes Q and U. Q = I t says where the charge came from if you know current and time.
Type 1e-4 and 10, click Calculate, and check 10 µF. Then 2e-6 and 5: 0.4 µF. The calculator divides Q by U; it does not guess a dielectric.
How to use
- In the first field enter Q in coulombs, for example 0.0001 or 1e-4. 1 µC is 1e-6.
- In the second field enter U in volts, for example 10.
- Click Calculate. 1e-4 C and 10 V give 10 µF. 2e-6 C and 5 V give 0.4 µF.
- U = 0 is rejected. Zero in Q at nonzero U gives C = 0. Both fields need a number.
- For energy, open E = ½ C U². Two C in series live on series capacitance.
Formula
C = Q / U
Units: F, C, V. U ≠ 0.
C, Q, and U on the capacitance card
One C from charge and voltage: C = Q/U. 1e-4 C at 10 V is 10 µF. 2e-6 C at 5 V is 0.4 µF.
- C
- Capacitance [F]. 10 µF is 1e-5 F. The quotient Q/U, not a C1+C2 network.
- Q
- Charge on the plates [C]. 1e-4 C at 10 V. Not current I.
- U
- Voltage between the plates [V]. U = 0 does not divide.
Real-life examples
Example 2
C = 4e-7 F.
Example 3
Q = 1e-9, U = 1 V -> 1 nF.
Example 4
Q = 2.3e-4 C.
Example 5
Q = 1.2e-4 C -> 10 µF.
Example 6
Q = 1e-3, U = 100 V.
Example 7
Typical filter cap.
Example 8
Q = 470e-9 C -> 470 nF.
Example 9
Fixed Q = 5e-5, U = 25 V.
Example 10
Result shows F and µF when C < 1 mF.
Ways to use this calculator
- You compute 10 µF from 1e-4 C and 10 V.
- You check 1 nF from 1e-9 C and 1 V.
Frequently asked questions
How much C at Q = 1e-4 C and U = 10 V?
Capacitance is 10 µF. You divide 0.0001 C by 10 V and get 1e-5 F.
How much at 2e-6 C and 5 V?
You get 0.4 µF, which is 4e-7 F. Two microcoulombs on five volts.
Which units do I type?
Charge Q [C], voltage U [V]. Result C [F]. 1 µC is 1e-6 C, not a 1 in field Q.
Is this C = ε0 A / d?
No. Here C comes from charge and voltage. ε0 A / d lives on the parallel-plate page when it is on the hub.
Where is energy?
On the capacitor-energy page. There E = ½ C U². Here only capacitance from Q and U.
Does a comma in 0.0001 work?
Yes. 0.0001, 0,0001 and 1e-4 mean the same Q [C]. C = Q / U stays the same.
Where are two C in series?
On the series-capacitance page. There you combine two C values. Here you compute one C = Q/U.
Is 1 F a lot?
Yes. A farad is huge. Everyday electronics uses µF and nF: 10 µF is 1e-5 F, 1 nF is 1e-9 F.
What about U = 0?
The calculator refuses zero volts. C = Q/U at zero voltage does not exist.
How much at 1 nC and 1 V?
Capacitance is 1 nF. 1e-9 C on 1 V is 1e-9 F, which the calculator can also show in nF.
Knowledge sources
The formula is the school one. Units follow SI; NIST SP 330 and BIPM define the measures, not your result.
Page updated in 2026.