# Capacitor Charge Time Calculator

URL: https://speedycalculator.com/calculators/physics/capacitor-charge-time/
Last updated: 2026-10-30

> The capacitor charge time calculator finds the RC time constant and the time a capacitor takes to charge to a chosen percentage of the supply voltage (or a number of time constants) through a resistor.

## Inputs

- Resistance R (kΩ, Ω, MΩ)
- Capacitance C (µF, nF, pF, mF, F)
- Target
- Charge level (%)
- Number of time constants

## Results

- Time constant τ
- Charging time
- Charge level reached

## Formula

```
τ = R·C,  t = −τ·ln(1 − p/100),  5τ ≈ 99.3%
```

## Explanation

A capacitor charging through a resistor never quite reaches full voltage – it gets 63.2% of the way in one time constant and 99.3% in five. Timers, debounce circuits and camera flashes rely on this predictable curve.

### How to use the Capacitor Charge Time Calculator

- **Resistance R**
- **Capacitance C**
- **Target**
- **Charge level (%)**
- **Number of time constants**

Results update as you type, every field has its own unit menu, and everything is calculated in your browser.

### How it works

Enter the resistance and capacitance, then the target charge percentage (or a number of time constants).

### Inputs explained

FieldWhat to enterResistance RUnits: kΩ, Ω, MΩCapacitance CUnits: µF, nF, pF, mF, FTargetChoose one: Percentage of supply voltage, Multiple of τCharge level (%)A numberNumber of time constantsA number

### Example values

How the main result changes when **Resistance R** changes and everything else stays at the example values above:

Resistance R (kΩ)Charging time (s)52.48097.53.7214104.961812.56.2023157.4428209.9237

## Worked example

Inputs — Resistance R: 10 kΩ; Capacitance C: 100 µF; Target: Percentage of supply voltage; Charge level (%): 99.3.

Results — Time constant τ = 1,000 ms; **Charging time = 4.96185 s**; Charge level reached = 99.3 %.

## Key terms

- **Time constant**: τ = RC.

## FAQ

**Why is 5τ considered fully charged?**
The capacitor is at 99.3% of the supply.

**Does discharging take as long?**
Yes – the same exponential with the same τ.

**What does τ mean physically?**
The time to reach 63.2% of the final voltage.

**How do I make a longer delay?**
Increase R or C.


## Sources

- [OpenStax – University Physics Volume 2](https://openstax.org/details/books/university-physics-volume-2)
- [HyperPhysics (Georgia State University)](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html)