High Pass Filter Calculator

What Is an RC High-Pass Filter?

A first-order RC high-pass filter passes high-frequency signals while attenuating low frequencies. It is built from a series capacitor and a shunt resistor to ground, common in audio coupling and DC blocking stages.

Cutoff Frequency

$$f_c = \frac{1}{2\pi RC}$$

At the cutoff frequency the output magnitude falls to about 70.7% of the input (-3 dB). Below $ f_c $ the signal rolls off at 20 dB per decade.

Design Workflow

Pick a target cutoff, then choose R and C values from standard component ranges. Alternatively, enter the parts you have and compute the resulting cutoff. The time constant $ \tau = RC $ sets how quickly the filter responds to step changes.

Frequently Asked Questions

What is the -3 dB point?

It is the cutoff frequency where power is halved, which corresponds to a voltage ratio of 1/√2 or about 0.707.

How do I block DC but pass audio?

Choose $ f_c $ well below your lowest audio frequency, for example 20 Hz for full-range audio coupling.

Can I solve for R or C?

Yes. Select the unknown you need and enter the other two values. The calculator rearranges $ f_c = 1/(2\pi RC) $ automatically.

Does load impedance matter?

This ideal formula assumes the load is much larger than R. Heavy loading shifts the effective cutoff.

What units should I use?

Resistance in ohms, capacitance in microfarads, and frequency in hertz. Internal math converts microfarads to farads.

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What Is an RC High-Pass Filter?

Cutoff Frequency

Design Workflow

Frequently Asked Questions

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