Voltage Divider Calculator
Calculate output amplitude and phase for resistor, capacitor, and inductor divider pairs using one consistent impedance model.
Divider inputs
Live result
Output voltage (V₂)
4.000 V
A 12.000 V input becomes 4.000 V across R₂.
Transfer ratio |V₂/V₁|
0.3333
Phase shift
0.00°
Circuit response
Passive divider
Calculation details
| Parameter | Value | Unit | Interpretation |
|---|---|---|---|
| Input voltage | 12.000 | V | Source amplitude |
| Resistance 1 | 2.000 | kΩ | First series component |
| Resistance 2 | 1.000 | kΩ | Output-side component |
| Transfer ratio | 0.3333 | V/V | Output amplitude divided by input amplitude |
| Phase shift | 0.00 | ° | Output relative to input |
| Output voltage | 4.000 | V | Voltage across Resistance 2 |
The model assumes ideal components connected in series and an unloaded output. Real loads can change the effective second impedance and therefore the measured voltage.
How to use the voltage divider calculator
What this calculator does
This calculator finds the amplitude of the voltage measured across the second component in a two-component series divider. It supports seven practical combinations: RR, CC, LL, RC, CR, RL, and LR. For mixed resistor-capacitor and resistor-inductor circuits, it also estimates the phase shift between the output and input. The calculation uses ideal impedances and therefore describes an unloaded divider. It does not automatically include source resistance, component tolerances, parasitic effects, or the impedance of a connected load.
When to use it
Use the tool to choose a resistor ratio for a sensor or analog-to-digital input, check a capacitive or inductive divider, estimate the attenuation of a first-order passive filter at one frequency, or verify hand calculations before selecting standard component values. The basic resistive relationship follows the standard voltage-divider derivation for series circuits.
How to calculate
- The calculator opens with a ready-to-use RR example: 12 V, 2 kΩ, and 1 kΩ. Its result and a validated example Excel workbook are available immediately.
- Choose a Divider type. The component labels and unit menus adapt to resistance, capacitance, or inductance while preserving the entered numeric values.
- Replace Input voltage (V₁), Component 1 value, and Component 2 value. Choose their adjacent unit controls rather than typing unit symbols in the value boxes.
- For RC, CR, RL, or LR, enter Frequency (f) and select the Frequency unit. Results update live as each valid value changes.
- Read Output voltage (V₂), Transfer ratio |V₂/V₁|, Phase shift, Circuit response, the displayed formula, and the calculation-detail table. Select Download Excel to export the current typed model. Reset clears the demonstration data and may disable export until a complete valid state is entered again.
Input guide
Divider type is required and chooses the series order. RR means resistor then resistor; CC means capacitor then capacitor; LL means inductor then inductor. RC and LR are low-pass arrangements because the output is taken across the capacitor or resistor respectively. CR and RL are high-pass arrangements because output is taken across the resistor or inductor. Reversing the letters changes which component is first and which is measured.
Input voltage (V₁) is a required nonnegative amplitude. Enter plain decimal numbers such as 12 or correctly grouped values such as 1,200.5. The accepted decimal separator is a period; scientific notation and embedded unit symbols are rejected. Voltage unit is required and can be mV, V, or kV. Changing the unit converts the current value so the physical voltage remains unchanged.
Component 1 value and Component 2 value are required positive numbers. Their visible circuit labels become Resistance 1/2, Capacitance 1/2, or Inductance 1/2 according to the selected topology. Component 1 unit and Component 2 unit are required: Ω, kΩ, or MΩ for resistance; pF, nF, µF, or mF for capacitance; and µH, mH, or H for inductance. A zero component is rejected because it creates a degenerate ideal circuit. A common mistake is forgetting that a capacitive divider ratio is inverted relative to raw capacitance: a larger capacitance has a smaller impedance.
Frequency (f) and Frequency unit are required only for mixed RC, CR, RL, and LR modes. Enter a positive value such as 1 kHz. Frequency changes capacitive and inductive reactance, so it changes both attenuation and phase. It is intentionally hidden for RR, CC, and LL because frequency cancels from the ideal ratio. The unit symbols used here follow the coherent electrical and frequency units summarized by NIST's SI derived-unit guidance.
Output guide
Output voltage (V₂) is the calculated amplitude across the second component, shown in the selected voltage unit. Transfer ratio |V₂/V₁| is a dimensionless amplitude ratio. In these passive ideal divider modes it stays from 0 to 1. Phase shift is measured in degrees: zero means output and input are in phase, a negative value means output lags, and a positive value means output leads. Circuit response identifies the topology as a passive divider, low-pass, or high-pass arrangement. The live summary pills repeat the same canonical type, ratio, output, and phase values; they are not separate calculations.
The Calculation details table reports each current input, its selected unit, transfer ratio, phase, and output. Mixed modes also show frequency and angular frequency. Every table row and workbook value comes from the same model as the primary result. The formula line identifies the equation used for the selected topology.
Worked example
The startup example uses an RR divider with V₁ = 12 V, R₁ = 2 kΩ, and R₂ = 1 kΩ. The transfer ratio is R₂ ÷ (R₁ + R₂) = 1 ÷ (2 + 1) = 0.333333.... Multiplying by the input gives V₂ = 12 × 0.333333... = 4.000 V. Because ideal resistors do not create a phase shift, the displayed phase is 0.00°. The first-open pills, result cards, table, and Excel checkpoints all use these same values.
How the impedance model works
The general rule is V₂ = V₁ × Z₂ ÷ (Z₁ + Z₂), where Z represents impedance. A resistor has impedance R, a capacitor has impedance 1/(jωC), and an inductor has impedance jωL. For two capacitors or two inductors, the common frequency terms cancel. In mixed circuits, the transfer function is complex, so the calculator separates magnitude from phase. Gain and phase are the two quantities normally used to describe frequency response; a concise overview is available in the LibreTexts introduction to Bode plots.
Practical interpretation and common mistakes
For RR dividers, only the resistance ratio controls ideal output voltage, but the absolute resistance values still control divider current and susceptibility to loading. Very small resistances waste power; very large resistances can make source and load impedance errors more important. For low-pass RC or LR arrangements, raising frequency reduces output amplitude. For high-pass CR or RL arrangements, raising frequency increases output amplitude toward the input. An output ratio near 0 means strong attenuation, while a ratio near 1 means little attenuation.
Do not use this ideal calculator as a power supply design by itself. A divider is best for reference and signal-level applications with light loading. Component tolerances, capacitor equivalent series resistance, inductor winding resistance, and source impedance can shift real results. Also distinguish signal amplitude from RMS or peak-to-peak voltage: the ratio is unchanged when the same voltage convention is used consistently, but the displayed absolute value follows the number you enter.