RC Time Constant

Calculate RC time constants and charge or discharge curves

About this calculator

The RC Time Constant Calculator finds the time constant τ = R·C of a resistor–capacitor circuit and evaluates the exponential charge curve V(t) = Vin·(1 − e^(−t/τ)) or discharge curve V(t) = Vin·e^(−t/τ) at any moment. It accepts resistance in Ω, kΩ, or MΩ and capacitance in F, µF, nF, or pF, reports the voltage and percentage at time t, the 5τ settling time, and tabulates the curve from 0 to 5τ.

How to use the RC Time Constant calculator

  1. Enter the quantities you know, using the units shown on each field.
  2. Read the computed results — they update instantly as you type.
  3. Use the visual explanation to see how the quantities relate.
  4. Copy the page URL to share the exact calculation.

Common examples

  • R = 10 kΩ, C = 100 µF → τ = 1 s; charging 5 V reaches 3.1606 V (63.21%) at t = 1 s
  • R = 1 kΩ, C = 1000 µF, 12 V charge → 7.5854 V after one time constant, ≈ full at 5τ = 5 s
  • R = 4.7 kΩ, C = 10 µF, discharging 9 V → τ = 0.047 s, 3.3109 V (36.79%) left at t = τ
  • R = 1 MΩ, C = 1 µF → τ = 1 s, fully settled (5τ) in 5 s

Frequently asked questions

How does the RC Time Constant calculator work?

Enter the known quantities and the calculator applies the governing physical law or scientific formula to find the unknowns, stating the equation it used and the units of every result. Computations run at high precision.

When would I use the RC Time Constant calculator?

It suits physics and chemistry homework, lab work, engineering estimates, and any time you want to explore how changing one quantity affects the others in a well-defined scientific relationship.

How accurate are the results?

The formula itself is evaluated at 30 significant digits of precision. Keep in mind that idealized models — such as neglecting friction, air resistance or measurement error — bound the real-world accuracy more than the arithmetic does.

Can I share a specific calculation with someone else?

Yes. Every value you enter updates the URL, so copying the address bar and sharing the link reopens the exact same calculation for whoever clicks it.