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Enter your values, then click Calculate result.How this calculator helps
Calculate ideal first-order RC cutoff, time constant and low-pass or high-pass amplitude at a supplied frequency with unit checks. Low-pass mode describes output across the capacitor of an ideal series RC stage. High-pass mode describes output across the resistor in the corresponding ideal arrangement. Both have the same corner frequency but different response away from it. Selecting a mode changes the modeled output; it does not rewire an actual circuit or confirm that your measured node has the assumed topology.
How to use it
- 1
Prepare the independently established inputs in the units shown, starting with topology matters.
- 2
Review capacitance units and the supported scope before submitting; example defaults demonstrate the arithmetic rather than a personal recommendation.
- 3
Click Calculate result to submit the current values. Input edits retain the previous submitted result until you calculate again.
- 4
Read the labeled output with the worked example, then check real circuit checks before using the result in another record.
Formula and methodology
τ=RC with C in farads; f꜀=1/(2πRC). For x=2πfRC, low-pass magnitude=1/√(1+x²), high-pass magnitude=x/√(1+x²). Gain dB=20log₁₀(magnitude).
The calculator applies the displayed arithmetic to the values entered on this device. It does not silently load a local tax rate, currency conversion or commercial assumption.
Worked calculation example
R=1,000 Ω and C=100 nF give τ=0.1 ms and cutoff≈1,591.54943 Hz. At 1,000 Hz, the ideal low-pass amplitude ratio is about 0.846733 and the high-pass ratio about 0.532018. At cutoff, either magnitude is 1/√2.
How to interpret your result
R=1,000 Ω and C=100 nF give τ=0.1 ms and cutoff≈1,591.54943 Hz. At 1,000 Hz, the ideal low-pass amplitude ratio is about 0.846733 and the high-pass ratio about 0.532018. At cutoff, either magnitude is 1/√2. Single unloaded passive first-order RC stage. No component selection, active-filter design, loading correction or electrical safety approval. Compare the labeled intermediate outputs with the input units and convention before carrying a number into another worksheet.
For different inputs or formulas, use Ohm’s Law, Watt and Ampere Calculator; Voltage Drop Calculator.
Related questions this calculator covers
- rc filter calculator
Scenario comparison
| Scenario | What it shows |
|---|---|
| Cutoff check | at f=1/(2πRC), both ideal magnitudes are approximately 0.70710678. |
| DC check | low-pass magnitude is one and high-pass magnitude is zero. |
| Resistance change | doubling R with the same C halves cutoff and doubles the time constant. |
Common mistakes to avoid
- Entering microfarads as if they were nanofarads.
- Treating the corner frequency as a complete signal cutoff.
- Ignoring source/load impedance while applying an unloaded formula.
Source resistance, load impedance, capacitor tolerance, parasitic effects and measurement equipment can change the observed response. Compare the actual circuit against the assumed single stage before applying this worksheet. Cascading stages without isolation does not automatically equal multiplying ideal isolated gains. Use measured component values for a comparison, and verify a real design with appropriate circuit analysis and safe measurement practice.
Authoritative reference. Method reference reviewed on 4 October 2026. The displayed worksheet and examples are SolvePilot’s own bounded implementation. The reference does not certify an individual calculation. Review by Mohammad Qasim is editorial and technical, not patient-specific, financial, structural or equipment approval.What can affect the result?
Topology matters
Low-pass mode describes output across the capacitor of an ideal series RC stage. High-pass mode describes output across the resistor in the corresponding ideal arrangement. Both have the same corner frequency but different response away from it. Selecting a mode changes the modeled output; it does not rewire an actual circuit or confirm that your measured node has the assumed topology.
Capacitance units
The field uses nanofarads, while the formula uses farads. The implementation multiplies the entered capacitance by one billionth before calculating RC. A 100 nF capacitor is 0.0000001 F. Entering microfarads as if they were nanofarads shifts the corner frequency by a factor of one thousand, so compare the component marking and its unit carefully.
Cutoff versus stopband
The corner is the point where ideal amplitude falls to approximately 0.707 of the relevant passband reference, or about −3.0103 dB. It is not a frequency beyond which the signal becomes zero. A first-order response changes gradually. The selected evaluation frequency lets you inspect one point rather than treating the cutoff as a brick-wall boundary.
Amplitude and decibels
The displayed ratio is a voltage-amplitude magnitude under the unloaded model. Its decibel expression uses twenty times the base-ten logarithm. It is not a phase response or a direct power ratio for arbitrary impedances. At zero frequency, the ideal high-pass magnitude is zero and the logarithmic gain is negative infinity; that is a defined model boundary rather than a numeric crash.
Real circuit checks
Source resistance, load impedance, capacitor tolerance, parasitic effects and measurement equipment can change the observed response. Compare the actual circuit against the assumed single stage before applying this worksheet. Cascading stages without isolation does not automatically equal multiplying ideal isolated gains. Use measured component values for a comparison, and verify a real design with appropriate circuit analysis and safe measurement practice.
Privacy and browser processing
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Accuracy and verification
Accuracy depends first on input quality. Confirm definitions, scales, dates and source information before entering a value. Keep an independent record of any result used for planning because this page does not create an official statement or retain a calculation history.
Limits of this estimate
Single unloaded passive first-order RC stage. No component selection, active-filter design, loading correction or electrical safety approval. The entered values are not independently verified. Numerical output does not establish the suitability of its assumptions for a real situation. Calculator inputs are processed locally in the browser interface; avoid entering identifying records and retain the relevant measurement or source basis with any result you save.
Sources and review information
Frequently asked questions
What capacitance unit is used?＋
Nanofarads. The formula converts it to farads internally.
Are low-pass and high-pass both supported?＋
Yes, for the stated single unloaded passive RC topology and one supplied evaluation frequency.
Is the cutoff a complete signal block?＋
No. It is the ideal corner point; attenuation is gradual for a first-order stage.
Why does high-pass show −∞ dB at zero Hz?＋
Its ideal DC amplitude is zero, whose logarithmic gain is negative infinity.
Does it include loading or tolerances?＋
No. Real source/load impedance and component variation require separate circuit review.