RC filter cutoff calculator
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Filter values
Cutoff frequency
−3 dB cutoff (fc)
fc = 1 ÷ (2π·R·C)
159.2 Hz
Phase shift at fc
Single RC section
-45°
A low-pass RC section is −3 dB at cutoff and rolls off at −20 dB/decade (above fc).
Reverse — component for a target cutoff
Required R (using C above)
R = 1 ÷ (2π·fc·C)
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Required C (using R above)
C = 1 ÷ (2π·fc·R)
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About RC filters
A single RC section is the building block of tone controls, anti-aliasing front-ends and DC blockers. It is first-order — only 20 dB/decade — so real designs cascade sections or use an op-amp stage for sharper roll-off. Capacitor tolerance (typically ±10 % or worse) directly moves the cutoff, so leave margin in a production design.
Building it? Find resistors and capacitors in our catalog.