03 // Bidirectional STEM Calculators // ENGINEERINGf_c = 1 / (2 × π × R × C)

RC Filter Cutoff Frequency & Time Constant Calculator

A first-order RC low-pass or high-pass filter reaches its half-power (-3.01 dB) corner frequency f_c where capacitive reactance X_C equals resistance R: f_c = 1 / (2 × π × R × C).

f_c = 1 / (2 × π × R × C)

Pick which value you want to calculate (or type into any field):Solving for: f_c — Cutoff Frequency (-3 dB)

Cutoff Frequency (-3 dB)Calculated

Half-power corner frequency in Hertz

0.1100,000,000.00

Filter Resistance

Series or shunt resistance in Ohms

110,000,000.00

Filter Capacitance

Capacitance in microfarads (switch inline unit for nF or pF)

1.0000e-610,000.00

Calculated Result · Cutoff Frequency (-3 dB) (f_c)

159.1549Hz

Converted units:

Step-by-Step Calculation

01Canonical Law: f_c = 1 / (2 × π × R × C)

02Given Inputs (Base Units): R = 1,000 Ω, C = 1 μF

03Solve for f_c (Cutoff Frequency (-3 dB)): f_c = 159.15 Hz

A first-order RC low-pass or high-pass filter reaches its half-power (-3.01 dB) corner frequency f_c where capacitive reactance X_C equals resistance R: f_c = 1 / (2 × π × R × C).

Real-World Reference Values

RC Time Constant (τ = R × C)τ = 1 / (2π f_c) = 1.00 ms

63.2% step-response charge time (5τ = 99.3% settled)

Roll-Off Slope-20 dB / decade (-6 dB / octave)

First-order single-pole attenuation rate

Phase Shift at f = f_cφ = ±45.0°

Output lags by 45° in low-pass, leads by 45° in high-pass

20-Row Comparison Table

Cutoff Frequency (-3 dB) (f_c) · Filter Resistance (R)

Compare across:

RC Filter Cutoff Frequency & Time Constant Calculator — Filter Resistance → Cutoff Frequency (-3 dB)
#	Filter Resistance (Ω)	Cutoff Frequency (-3 dB) (Hz)	Δ %
01	1,000.00 ΩCurrent	159.1549 Hz	0.00%
02	72,421.99 Ω	2.1976 Hz	-98.62%
03	144,842.99 Ω	1.0988 Hz	-99.31%
04	217,263.98 Ω	0.732542 Hz	-99.54%
05	289,684.97 Ω	0.549407 Hz	-99.65%
06	362,105.96 Ω	0.439526 Hz	-99.72%
07	434,526.96 Ω	0.366272 Hz	-99.77%
08	506,947.95 Ω	0.313947 Hz	-99.80%
09	579,368.94 Ω	0.274704 Hz	-99.83%
10	651,789.93 Ω	0.244181 Hz	-99.85%
11	724,210.93 Ω	0.219763 Hz	-99.86%
12	796,631.92 Ω	0.199785 Hz	-99.87%
13	869,052.91 Ω	0.183136 Hz	-99.88%
14	941,473.91 Ω	0.169049 Hz	-99.89%
15	1,013,894.90 Ω	0.156974 Hz	-99.90%
16	1,086,315.89 Ω	0.146509 Hz	-99.91%
17	1,158,736.88 Ω	0.137352 Hz	-99.91%
18	1,231,157.88 Ω	0.129273 Hz	-99.92%
19	1,303,578.87 Ω	0.122091 Hz	-99.92%
20	1,375,999.86 Ω	0.115665 Hz	-99.93%

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Frequently Asked Questions

How do I design an anti-aliasing RC filter for a 10 kHz ADC?+

Click SOLVE FOR on R (or C), set f_c to your desired corner frequency (e.g., 4 kHz), and choose a standard E24 capacitor value in nF or μF.

Why is the cutoff point called the -3 dB frequency?+

At f = f_c, output voltage drops to 1/√2 (≈ 0.7071) of input voltage, which equals 20 × log₁₀(1/√2) = -3.0103 dB (half power).

How is the RC time constant τ related to f_c?+

Since τ = R × C, the cutoff frequency is simply f_c = 1 / (2πτ) ≈ 0.159155 / τ.