RC Time Constant Calculator
τ = RC. Time for an RC circuit to charge to ~63% (or discharge to ~37%) of final value.
Result
Time constant τ
0.010000 s
10.0000 ms · 5τ = 0.0500 s (≈ fully charged).
- τ = RC10000 Ω × 1.000e-6 F
- τ in seconds0.01000000
- τ in ms10.0000
- 63% charged at0.0100 s
- 95% charged at0.0300 s (≈ 3τ)
- 99% charged at0.0500 s (≈ 5τ)
Step-by-step
- τ = R × C = 10000 × 0.000001 = 0.010000 s.
How to use this calculator
- Enter resistance in ohms.
- Enter capacitance in farads.
- Read τ in seconds and ms.
About this calculator
The RC time constant τ = RC characterizes how fast an RC circuit responds. After 1τ a charging capacitor reaches 1−1/e ≈ 63% of its final voltage; after 5τ it's at 99.3% (essentially "settled"). For discharge, the same constant governs how fast voltage falls to 1/e ≈ 37% of starting value.
Frequently asked
1 − 1/e ≈ 0.632. After τ seconds, a charging cap is at 63.2% of final voltage. Comes from solving the exponential charging equation.
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