RC Circuit Calculator

Created by Miłosz Panfil, PhD
Reviewed by Bogna Szyk and Steven Wooding
Last updated: Sep 25, 2022

Use this RC circuit calculator to compute the characteristic frequency of the RC circuit. You can also use it as a capacitor charge time calculator (RC time constant calculator) or an RC filter calculator. Depending on your need, the RC circuit can serve as a low pass filter or high pass filter.

RC circuit

The RC circuit is a fundamental electrical circuit in which a resistor of resistance R is connected in a series with a capacitor of capacitance CC.

Circuit diagram of a low pass RC filter.
Circuit diagram of a low pass RC filter. (Source: wikimedia.org.)

Such a circuit is characterized by a frequency ff and has two primary applications:

  • Low or high pass filter; and
  • Capacitor can be used to store the energy.

You can use our RC circuit calculator in the following ways:

  • RC filter calculator; or
  • Capacitor charge time calculator.

If you want to learn more about resistance and capacitance, check out our capacitor calculator and parallel plate capacitor calculator.

RC filter calculator

The characteristic frequency ff determines the frequency of signals that can flow through the circuit. The RC circuit suppresses frequencies smaller than ff, and signals with frequencies greater than ff can flow freely. However, this is not a clear-cut situation, and signals with frequencies around ff are still partially transmitted.

Depending on the configuration, you can use the RC filter to either filter out low or high frequencies. These are the high pass and low pass filters.

If you combine a low pass filter with a high pass filter, you get a broadband filter that suppresses all the signals below and above some frequencies. All of our music equipment is full of broadband filters.

Learn more about the characteristic frequency with our cutoff frequency calculator.

Capacitor charge time calculator

If we connect the RC circuit to a DC power supply, the capacitor will start to collect electric charge until it gets fully charged. The time it takes depends on the capacitance of the capacitor CC and the resistance of the resistor RR controlling the current, which is the amount of charge ending up in the capacitor per one second.

The larger the capacitance or the resistance, the longer it takes to charge the capacitor. Charging of the capacitor is an exponential process; the more charge there is, the longer it takes to gather more charge.

The capacitor charge time is the time it takes for the capacitor to get charged up to around 63%. If you double the time, you get about 87%. To check the capacitor charge time calculator, click the Advanced mode button under the calculator.

RC time constant calculator

The equation for the characteristic frequency ff of the RC circuit is:

f=12πRC\small f = \frac{1}{2\pi RC}

where:

  • RR – Resistance of the resistor (Ohms);
  • CC – Capacitance of the capacitor (Farads); and
  • ff – Characteristic frequency (Hertz).

To compute the frequency, specify the RC circuit's resistance and capacitance. You can also fix the frequency and, for example, the resistance to find the required capacitance.

The capacitor charge time tt equals:

t=RC\small t = R C

To check the capacitor charge time, open up the Advanced mode of the RC circuit calculator.

The timer functionalities of a 555 IC use the charge time of capacitors to define characteristic times of operations that are used in many applications. Check them out at our 555 timer calculator!

You can try also other calculators related to the electric circuits, such as the power factor calculator.

FAQ

What is an RC circuit?

An RC circuit is an electrical circuit made of capacitors and resistors, where the capacitor stores energy and the resistor manage the charging and discharging.

RC circuits are signal filters, blocking specific unwanted frequencies depending on the situation.

How can I calculate the capacitor charging time of an RC circuit?

It would be convenient to use a tool to calculate the capacitor charging time of an RC circuit, but you may also use the formula:

t = R × C

where:

  • t - Capacitor charge time;
  • R - Resistance of the resistor; and
  • C - Capacitance of the capacitor.

It means you may determine the charge time by multiplying the capacitance and resistance of the RC circuit.

Is RC time constant the same as capacitor charging time?

Yes, they are both the same. They might seem different, but only grammatically. RC time constant measures how fast the capacitor can be charged*, hence the term "capacitor charging time".

The RC time constant is the product of the circuit's capacitance and resistance, which is also how we calculate the capacitor's charging time.

Can I calculate the characteristic frequency of an RC circuit?

The characteristic frequency of an RC circuit determines the frequency of signals through the circuit. It is pretty simple to calculate once you know the formula.

f = 1/ 2π × R × C

Where:

  • R - Resistance of the resistor;
  • C - Capacitance of the capacitor; and
  • f - Characteristic frequency.

So, All you have to do is determine the product of 2, π (3.14), the resistance, and capacitance. Then divide one by the product.

Miłosz Panfil, PhD
Capacitance
μF
Resistance
Ω
Frequency
Hz
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