RC Time Constant Calculator
Find the time constant, cutoff and ideal charge times for a resistor-capacitor pair.
Your inputs
Calculation results
Formula & assumptions
τ = RC; cutoff = 1/(2πτ); ideal 95-percent charge time = −τ ln(0.05).
Values use the specified units. Calculations use floating-point arithmetic. Check input measurements and formula assumptions before applying the result.
Compare your scenarios
Save up to five results to compare changes side by side. Scenarios stay in this tab until you clear or reload it.
Using RC Time Constant Calculator
Find the time constant, cutoff and ideal charge times for a resistor-capacitor pair.
- Enter resistance, capacitance using the units printed under each field.
- Choose Calculate, or enable live updates. Review the result labels and formula assumptions.
- Save scenarios to compare up to five variations, then copy the report or download JSON or CSV.
Example
Resistance: 10000 ohms Capacitance: 100 microfarads Time constant · seconds: 1 Cutoff · hertz: 0.15915494 95-percent charge time · seconds: 2.9957323 99-percent charge time · seconds: 4.6051702
Questions & answers
What does RC Time Constant Calculator calculate?
Find the time constant, cutoff and ideal charge times for a resistor-capacitor pair.
Which units should I enter?
Resistance uses ohms. Capacitance uses microfarads. Convert values to these units before calculating.
Which formula does it use?
τ = RC; cutoff = 1/(2πτ); ideal 95-percent charge time = −τ ln(0.05).
What does the included example show?
Resistance: 10000 ohms; Capacitance: 100 microfarads. Result: Time constant · seconds = 1; Cutoff · hertz = 0.15915494; 95-percent charge time · seconds = 2.9957323; 99-percent charge time · seconds = 4.6051702.
Can I compare different settings?
Yes. Save a scenario, change the inputs and save another result. Up to five scenarios are compared in this tab; they disappear when you reload or leave.
Can I export the calculation?
Copy the JSON report or download JSON and CSV with inputs, result labels and numeric values. Processing uses local JavaScript; no calculation request is sent to our server. Displayed values use up to 10 significant digits; exports retain JavaScript numeric precision.
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