Free · Physics models
Ideal RC Charging Time
Relate resistance, capacitance and selected charging fractions for an initially uncharged ideal capacitor.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
A 1,000-ohm resistor and 1,000-microfarad capacitor have a one-second time constant; the five-time-constant selection takes five seconds.
τ=RC; charge fraction = 1−exp(−t/τ).
Worked example
Enter these known values and leave the other values blank.
- Resistance
- 1000 Ω
- Capacitance
- 1000 μF
- Time constant
- 1 sec
- Charging Time
- 5 sec
Assumptions and limitations
- Constant voltage step, initially uncharged ideal capacitor and fixed positive resistance and capacitance are assumed.
- Five time constants is about 99.3% charging, not exactly complete charging. The menu labels are rounded fractions. Selecting a fraction activates its multiplier control; changing that multiplier overrides the number of time constants while the preset label stays fixed. The custom fraction uses the exponential relation.
- Leakage, equivalent series resistance, dielectric absorption and nonlinear components are omitted.
- Clear the unknown numerical field before using a supported inverse; selection controls retain their captured branches.
Common questions
What assumptions matter for this model?
Constant voltage step, initially uncharged ideal capacitor and fixed positive resistance and capacitance are assumed.
What does this model leave out?
Leakage, equivalent series resistance, dielectric absorption and nonlinear components are omitted.
References
Model requirements: Resistance must be positive. Capacitance must be positive. Finite charging fraction must lie from zero up to but excluding one. Select the charging-time equation from the visible percentage branch and its retained multiplier control; the captured graph leaves the five-time-constant result stale after changing the percentage selector.