This RC time constant calculator finds the RC time constant and the energy stored in a capacitor. Enter resistance, capacitance, and voltage above for instant results.
Formulas
Time constant τ = R × C Stored energy E = ½ × C × V²
Example
R = 10 kΩ, C = 100 µF, V = 12 V: τ = 10,000 × 0.0001 = 1.0 s; E = 0.5 × 0.0001 × 12² = 7.2 mJ.
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Frequently Asked Questions
What is the RC time constant?
It is tau = R x C, the time for a capacitor to charge to about 63% of the supply voltage. A capacitor is nearly full after five time constants.
How do I calculate energy stored in a capacitor?
Use one half times capacitance times voltage squared (E = 0.5 x C x V^2).
How long to fully charge a capacitor?
About five time constants. With a 1-second tau, that is roughly 5 seconds to reach 99%.