Electrical & Controls
RC time constant calculator
Time constant and charge time for a resistor–capacitor circuit.
Calculating…
How it's calculated
τ = R × C
fc = 1 ÷ (2π × R × C)
After one time constant a charging capacitor reaches about 63% of the supply voltage. After five it is effectively fully charged (99.3%). The same timing applies to discharge.
This is useful for input filters, delay circuits and working out how long a capacitor takes to bleed down through a discharge resistor.