RC Low-Pass / High-Pass Filter Calculator – Cutoff Frequency
A resistor and a capacitor make the simplest filter. Below the cutoff a low-pass passes signals through; above it they roll off at 20 dB per decade. Swap the parts around and you get a high-pass.
Ω
= 1 kΩF
= 100 nF100n = 100 nF, 4u7 = 4.7 µFHz
= 10 kHzResults
- Cutoff frequency (−3 dB)
- 1.592 kHz
- Time constant τ
- 100 µs
- Settling time (5τ)
- 500 µs
- Gain at 10 kHz
- -16.07 dB
- Phase at 10 kHz
- -80.96°
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Cutoff frequency (−3 dB): 1.592 kHz
Formula
- fc = 1 / (2π·R·C)
- τ = R·C
- |H| = 1/√(1+(f/fc)²) (low-pass)
FAQ
- What is the −3 dB point?
- It is the frequency where output power is halved, which means the voltage is about 70.7% of the input.
- How long does the capacitor take to charge?
- About 5τ to reach 99%. The calculator shows 5τ for you.