How to use the rc time constant calculator
Find time constant and charge time of an RC circuit. Enter resistance, capacitance, supply voltage in the fields above; the time constant τ, time to 99% charge, cutoff frequency are computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- R — Resistance (kΩ)
- C — Capacitance (µF)
- V — Supply voltage (V)
Worked example
With resistance = 10 kΩ, capacitance = 100 µF, supply voltage = 5 V, the calculator gives time constant τ ≈ 1,000 ms; time to 99% charge ≈ 5,000 ms; cutoff frequency ≈ 0.1591549 Hz.
Frequently asked questions
What is the formula for the rc time constant calculation?
Time constant τ (ms) = R × C. Time to 99% charge (ms) = 5 × [Time constant τ]. Cutoff frequency (Hz) = 1000 / (2 × π × [Time constant τ]). Here R is resistance (kΩ), C is capacitance (µF), V is supply voltage (V).
What inputs do I need for the rc time constant calculator?
You need resistance in kΩ, capacitance in µF, supply voltage in V. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.