Voltage Divider Calculator

Introduction

A voltage divider is one of the most basic and useful circuits in electrical engineering. It uses two or more components connected in series to split an input voltage into a smaller output voltage. Engineers use voltage dividers every day to set reference voltages, read sensors, and scale signals to safe levels for microcontrollers and other electronics.

This Voltage Divider Calculator lets you quickly find the output voltage, component values, or input voltage for several types of divider circuits. It supports resistive, capacitive, inductive, RC low-pass, CR high-pass, RL low-pass, LR high-pass, and LC resonant configurations. Simply enter any three known values, and the calculator solves for the missing one. It also shows the divider ratio, current through the circuit, power dissipated, and a clear circuit diagram so you can see exactly how the components are arranged.

For AC divider types, the tool calculates phase shift, gain in decibels, and cutoff or resonant frequency. You can also expand the advanced section to add a load resistance, which shows how a real-world load affects your output voltage. Whether you are a student learning circuit basics or a working engineer designing a filter, this calculator gives you fast, accurate results without any manual math.

How to use our Voltage Divider Calculator

Enter your known circuit values and this calculator will find the missing value, along with the divider ratio, current, power dissipation, and more. It supports resistive, capacitive, inductive, and filter-based divider types.

Divider Type — Choose the type of voltage divider you want to calculate. Options include Resistive, Capacitive, Inductive, RC Low-Pass, CR High-Pass, RL Low-Pass, LR High-Pass, and LC Resonant. The input fields will change based on your selection.

V_in (Source Voltage) — Enter the input voltage applied to your divider circuit. You can pick millivolts (mV), volts (V), or kilovolts (kV) from the dropdown. Leave this blank if you want the calculator to solve for it.

V_out (Output Voltage) — Enter the desired or known output voltage taken across the lower leg of the divider. Select your unit from mV, V, or kV. Leave this blank if you want the calculator to find it for you.

R1 / R2 (Resistors) — For resistive dividers, enter the resistance values for R1 (upper, series element) and R2 (lower element where output is measured). Choose from ohms (Ω), kilohms (kΩ), or megohms (MΩ). Leave one blank to have it calculated. If you need to find the combined resistance of resistors wired in parallel before entering a value here, use our Parallel Resistor Calculator.

C1 / C2 (Capacitors) — For capacitive or filter-based dividers, enter the capacitance values. Units include picofarads (pF), nanofarads (nF), microfarads (µF), and millifarads (mF). For more detailed capacitor analysis, see our Capacitor Calculator.

L1 / L2 (Inductors) — For inductive or filter-based dividers, enter the inductance values. Units include microhenries (µH), millihenries (mH), and henries (H).

Frequency (f) — This field appears for all AC-based divider types. Enter the signal frequency and select hertz (Hz), kilohertz (kHz), or megahertz (MHz). Frequency is needed to calculate impedance for capacitors and inductors.

Advanced: Load Resistance (R_load) — Click the advanced toggle to add an optional load resistance in parallel with the lower leg. This lets you see how a real load affects your output voltage. Enter the value in Ω, kΩ, or MΩ.

Calculate and Reset — Press "Calculate" to run the computation. The results table will show the output voltage, divider ratio, current through the divider, power dissipated, and — for AC modes — the phase shift, gain in decibels, cutoff frequency, or resonant frequency. Press "Reset" to return all fields to their default values.

What Is a Voltage Divider?

A voltage divider is a simple circuit that turns a larger voltage into a smaller one. It uses two components connected in series to split an input voltage (V_in) into a lower output voltage (V_out). Voltage dividers are one of the most common and useful circuits in electrical engineering, found in everything from sensor readings to audio controls to power supply feedback loops.

How Does a Voltage Divider Work?

In the most basic form, a resistive voltage divider uses two resistors. The input voltage is applied across both resistors, and the output voltage is measured across the second resistor (R2). The formula is:

V_out = V_in × R2 / (R1 + R2)

The output voltage depends on the ratio between R2 and the total resistance (R1 + R2). If both resistors are equal, the output is exactly half the input. If R2 is much smaller than R1, the output will be much lower than the input. No active components like transistors or op-amps are needed — just two passive components and a voltage source. This relationship is a direct application of Ohm's Law, which relates voltage, current, and resistance in any circuit.

Types of Voltage Dividers

While resistive dividers are the most common, voltage dividers can also be built with other components that work with AC (alternating current) signals:

• Resistive: Uses two resistors. Works with both DC and AC signals. The output depends only on resistance values, not frequency. When working with multiple resistors in parallel before they connect to your divider, a Parallel Resistor Calculator can help you find the equivalent resistance.
• Capacitive: Uses two capacitors. The voltage split depends on capacitance values and the signal frequency. These are often used in high-voltage measurement circuits. Our Capacitor Calculator can help you analyze individual capacitor behavior.
• Inductive: Uses two inductors. Like capacitive dividers, the output depends on frequency. Used in RF and power applications.
• RC Low-Pass: Uses a resistor and capacitor. This divider passes low-frequency signals and reduces high-frequency signals, acting as a basic filter.
• CR High-Pass: Uses a capacitor and resistor. It does the opposite of a low-pass — it passes high frequencies and blocks low ones.
• RL Low-Pass / LR High-Pass: Similar to RC/CR filters but use an inductor instead of a capacitor.
• LC Resonant: Uses an inductor and capacitor. This type has a resonant frequency where the circuit behavior changes dramatically, useful in tuning and radio circuits.

Important Things to Know

Loading effect: A voltage divider works best when the load connected to the output draws very little current. If a heavy load (low resistance) is connected across V_out, it acts in parallel with the lower component, which changes the effective resistance and lowers the output voltage. This is why it's important to consider load resistance in real designs.

Power dissipation: Current flows through the divider at all times, which means the resistors constantly use power. For battery-powered circuits, you should use high-value resistors to keep this wasted power low. Understanding how power relates to voltage and current is essential — our Force Calculator and other physics tools can help reinforce these fundamental relationships.

Cutoff frequency: For RC, CR, RL, and LR dividers, there is a specific cutoff frequency where the output drops to about 70.7% (−3 dB) of the input. Below or above this frequency (depending on the filter type), the signal passes through with little change.

Common Uses for Voltage Dividers

• Reading sensor voltages with a microcontroller that requires a lower voltage range
• Setting a reference voltage for comparators or ADCs (analog-to-digital converters)
• Providing feedback in voltage regulator circuits
• Level shifting between circuits that operate at different voltages
• Building simple audio attenuators and volume controls
• Filtering signals in basic low-pass and high-pass configurations

Frequently Asked Questions

What is the voltage divider formula for two resistors?

The formula is Vout = Vin × R2 / (R1 + R2). R1 is the top resistor connected to the input voltage, and R2 is the bottom resistor where the output voltage is measured. The output is always less than or equal to the input.

Can I solve for a missing resistor value instead of Vout?

Yes. Enter any three of the four values (Vin, Vout, R1, R2) and leave one blank. The calculator will solve for the missing value. The calculated field will be highlighted in orange so you can see which one was computed.

Why is my output voltage lower than expected when I connect a load?

A load resistance connected across the output sits in parallel with R2. This lowers the effective resistance of the bottom leg, which reduces the output voltage. Use the Advanced section to add your load resistance and see the loaded output voltage.

What happens if R1 and R2 are equal?

When R1 equals R2, the output voltage is exactly half of the input voltage. The divider ratio is 0.5. For example, if Vin is 12V and both resistors are 10kΩ, Vout will be 6V.

Does a voltage divider work with DC and AC signals?

A resistive voltage divider works with both DC and AC signals because resistors do not change their behavior with frequency. Capacitive, inductive, and filter-based dividers only work properly with AC signals because their impedance depends on frequency.

What is the cutoff frequency shown in the results?

The cutoff frequency is the point where the output drops to about 70.7% of the input, which equals -3 dB. For an RC low-pass filter, it is calculated as fc = 1 / (2π × R × C). Signals below this frequency pass through easily, while signals above it get reduced.

What does the phase shift result mean?

Phase shift tells you how much the output signal is shifted in time compared to the input signal. It is measured in degrees. A 0° phase shift means the output and input are perfectly aligned. Capacitors and inductors cause phase shifts in AC circuits.

What does gain in dB mean?

Gain in decibels (dB) measures how much the signal is reduced by the divider. A passive voltage divider always has negative or zero dB gain because it can only reduce voltage, not amplify it. The formula is Gain (dB) = 20 × log10(Vout / Vin).

Why do I need to enter a frequency for capacitive and inductive dividers?

Capacitors and inductors have impedance that changes with frequency. A capacitor's impedance goes down as frequency goes up, and an inductor's impedance goes up as frequency goes up. Without knowing the frequency, the calculator cannot determine the impedance and thus cannot compute the output voltage.

What is the resonant frequency in an LC divider?

The resonant frequency is where the inductor and capacitor impedances are equal and cancel each other out. It is calculated as f0 = 1 / (2π × √(L × C)). At this frequency, the circuit behavior changes significantly and can produce very high or very low output depending on the configuration.

How do I keep power dissipation low in a voltage divider?

Use higher resistor values. The current through the divider equals Vin divided by (R1 + R2). Larger resistors mean less current and less wasted power. For example, using 100kΩ resistors instead of 1kΩ resistors reduces power dissipation by 100 times.

Can a voltage divider increase voltage?

No. A passive voltage divider can only reduce voltage or keep it the same. The divider ratio is always between 0 and 1, so Vout is always less than or equal to Vin. To increase voltage, you need an active circuit like a boost converter or amplifier.

What is the difference between RC low-pass and CR high-pass modes?

In an RC low-pass filter, the resistor is the top element and the capacitor is on the bottom. It lets low frequencies pass and blocks high frequencies. In a CR high-pass filter, the capacitor is on top and the resistor is on the bottom. It lets high frequencies pass and blocks low frequencies.

How accurate is this calculator for real circuits?

This calculator gives ideal results based on perfect components. Real resistors, capacitors, and inductors have tolerances (typically 1% to 20%) that cause small differences. Parasitic effects, temperature changes, and PCB layout can also affect real-world results. For most designs, the calculated values are a very good starting point.

What units can I use in this calculator?

Voltage supports mV, V, and kV. Resistance supports Ω, kΩ, and MΩ. Capacitance supports pF, nF, µF, and mF. Inductance supports µH, mH, and H. Frequency supports Hz, kHz, and MHz. Select the unit that matches your component values from the dropdown next to each input.