Electrical calculator
RC Time Constant Calculator
Calculate the time constant and charge/discharge times for an RC circuit.
About the rc time constant calculator
The RC time constant calculator finds how quickly a capacitor charges or discharges through a resistor.
How to use this calculator
- 1
Enter resistance
Enter the resistor value in ohms.
- 2
Enter capacitance
Enter the capacitor value in microfarads.
- 3
View results
See the time constant (τ) and charge times at 63%, 95%, and 99%.
How the calculation works
τ = R × C. Full charge ≈ 5τ. At 1τ: 63.2% charged. At 3τ: 95% charged.
Example: 10kΩ and 100µF: τ = 1s, full charge ≈ 5s.
Safety first
These calculators provide estimates based on standard formulas and NEC guidelines. Always verify results with a licensed electrician before making installations. Electrical work can be dangerous — never work on live circuits, and always follow local building codes and regulations.
Understanding electrical units
Voltage (V) is electrical pressure, current (A) is flow rate, resistance (Ω) opposes flow, and power (W) is the rate of energy use. Ohm's law (V = I × R) relates the first three, while power formulas (P = VI, P = I²R) connect all four. Understanding these relationships is key to safe electrical design.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about rc time constant calculator
How accurate is the RC time constant calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.