Case 1
- Resistance R (Ω)
- 10000Ω
- Capacitance C (F)
- 0.0001F
1.000000s
Open with these valuesRC Time Constant Calculator
1.000000s
Result: 1.000000 sOhms times farads give seconds directly: 10 kΩ with 100 µF (0.0001 F) has a time constant of 1 s. After one time constant the capacitor has reached about 63 % of the final voltage, after five it counts as full. Enter farads, not microfarads — 1 µF is 0.000001 F.
The numbers at a glance
Held fixed: Resistance R (Ω) 10,000.000 Ω.
| Capacitance C (F) (F) | Result (s) |
|---|---|
| 0.000025000000 | 0.250000 |
| 0.000050000000 | 0.500000 |
| 0.000075000000 | 0.750000 |
| 0.000100000000Your value | 1.000000 |
| 0.000125000000 | 1.250000 |
| 0.000150000000 | 1.500000 |
| 0.000175000000 | 1.750000 |
| 0.000200000000 | 2.000000 |
Worked examples
Case 2
- Resistance R (Ω)
- 470Ω
- Capacitance C (F)
- 0.000001F
0.000470s
Open with these valuesCase 3
- Resistance R (Ω)
- 2200Ω
- Capacitance C (F)
- 0.0000047F
0.010340s
Open with these valuesHow it's calculated
τ = R × C
- StepEnter the resistance in ohms — a 10 kΩ resistor is 10000 Ω.
- StepEnter the capacitance in farads — 100 µF is 0.0001 F.
- ResultRead the time constant in seconds; five times that counts as settled.
Reference table
| R (Ω), C (F) | What it is | Time constant (s) |
|---|---|---|
| 470, 0.000001 | 470 Ω with 1 µF | 0.00047 |
| 2200, 0.0000047 | 2.2 kΩ with 4.7 µF | 0.01034 |
| 1000, 0.001 | 1 kΩ with 1000 µF | 1 |
| 10000, 0.0001 | 10 kΩ with 100 µF | 1 |
| 100000, 0.00001 | 100 kΩ with 10 µF | 1 |
Questions
What is the RC time constant?
It is the product of resistance and capacitance, τ = R × C, in ohms times farads and therefore in seconds. It sets how fast the circuit charges and discharges. For 10 kΩ and 100 µF that is 10000 × 0.0001 = 1 s.
Why 63 % after one time constant?
Charging follows an exponential curve, not a straight line. After one time constant the capacitor sits at 1 minus 1 over e, about 63.2 % of the final voltage; discharging leaves it at about 36.8 %. The figure comes straight from the exponential, not from measurement.
How long does the capacitor take to charge fully?
In theory it never quite arrives, but five time constants are treated as full: the capacitor is then at about 99.3 %. A circuit with a 1 s time constant is settled after roughly 5 s. That threshold is an engineering convention, not a physical boundary.
What changes if I use a bigger resistor or capacitor?
Both slow the circuit down, and in direct proportion: doubling either value doubles the time constant. A larger resistor limits how fast charge can flow in, and a larger capacitor needs more charge for the same voltage. Shrink R or C to speed things up.
Do I enter farads or microfarads?
Farads. A 100 µF capacitor is 0.0001 F and a 1 µF capacitor is 0.000001 F. Entering raw microfarads would put the answer a million times too high.
Sources and last check
Information, not professional advice.