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RC Time Constant Calculator
Enter resistance and capacitance to find the RC time constant and related values.
Time constant (\u03c4)
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Time to 63.2% (1\u03c4)
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Time to 99.3% (5\u03c4)
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Cutoff frequency (-3dB)
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\u03c4 = R \u00d7 C. The capacitor reaches 63.2% charge in 1\u03c4, 86.5% in 2\u03c4, 95.0% in 3\u03c4, 98.2% in 4\u03c4, and 99.3% in 5\u03c4. Cutoff frequency fc = 1 / (2\u03c0RC).
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Understanding RC Time Constants
An RC circuit combines a resistor and capacitor. The time constant \u03c4 (tau) equals R \u00d7 C and determines how quickly the capacitor charges or discharges.
In one time constant, a capacitor charges to 63.2% of the applied voltage. It takes approximately 5 time constants to reach 99.3% (considered fully charged for most practical purposes).
RC circuits are used as filters, timing circuits, and smoothing circuits. The cutoff frequency fc = 1/(2\u03c0RC) defines where the filter attenuates the signal by 3dB.