Tip: Leave the optional frequency blank if you only want cutoff frequency.
What this high pass filter calculator does
This calculator is designed for a standard first-order RC high-pass filter. It helps you quickly compute:
- Cutoff frequency from resistor and capacitor values
- Required resistor for a target cutoff frequency
- Required capacitor for a target cutoff frequency
- Optional gain and phase at a specific test frequency
A high-pass filter attenuates low-frequency signals and allows higher frequencies to pass. It is widely used in audio circuits, sensor signal conditioning, and analog front-end design.
Core formula for a first-order RC high-pass filter
The key relationship is:
fc = 1 / (2πRC)
Where:
- fc = cutoff frequency in hertz (Hz)
- R = resistance in ohms (Ω)
- C = capacitance in farads (F)
At the cutoff frequency, the output amplitude is approximately 70.7% of the passband value (−3 dB point).
Frequency response equations
If you provide a test frequency, the calculator uses:
|H(jω)| = (ωRC) / √(1 + (ωRC)2)
Gain(dB) = 20 log10(|H(jω)|)
Phase = tan-1(1 / (ωRC)) in degrees
Here, ω = 2πf. These equations are for the classic RC high-pass configuration with output measured across the resistor.
How to use the calculator
1) Find cutoff frequency
- Select Find cutoff frequency from R and C.
- Enter resistor value and choose its unit.
- Enter capacitor value and choose its unit.
- Optionally add a test frequency to evaluate gain and phase.
2) Find resistor value
- Select Find resistor from fc and C.
- Enter your target cutoff frequency and capacitor value.
- The tool returns the required resistance.
3) Find capacitor value
- Select Find capacitor from fc and R.
- Enter target cutoff frequency and known resistor value.
- The tool returns the required capacitance.
Practical design tips
Use standard component values
Real components come in preferred E-series values (E12, E24, etc.). After calculating the ideal value, pick the nearest standard part and re-check the actual cutoff frequency.
Watch component tolerances
A 5% resistor and a 10% capacitor can shift cutoff frequency noticeably. If frequency precision matters, use tighter-tolerance components or trim/calibrate in software.
Account for loading effects
If the filter output is connected to a low-impedance load, the effective resistance changes and the actual response shifts. Buffering with an op-amp can protect your designed cutoff.
Choose realistic R and C ranges
- Very large R values can increase noise sensitivity.
- Very small C values can make parasitics significant.
- For many audio/sensor applications, kΩ and nF/µF ranges are practical.
Example
Suppose you choose R = 1 kΩ and C = 0.1 µF. Then:
fc = 1 / (2π × 1000 × 0.1×10-6) ≈ 1591.55 Hz
So frequencies much lower than about 1.6 kHz will be strongly attenuated, while frequencies above that region pass with less attenuation.
When to use a high-pass filter
- Remove DC offset before amplification
- Block low-frequency rumble in audio paths
- Suppress slow baseline drift in sensor signals
- Create crossover networks in speaker systems
Final note
This calculator gives mathematically correct ideal results for first-order RC design. In real circuits, PCB layout, source impedance, load impedance, and component tolerances all influence final behavior. Use simulation or measurement to validate critical designs.