This calculator finds the output voltage from any two-resistor divider the moment you enter the input voltage and both resistor values, using the same Vout = Vin × R2/(R1+R2) relationship every voltage divider follows. Use it to scale a higher voltage down to a level a microcontroller, sensor, or measurement circuit can read safely, without working the algebra by hand.
Basic 2-Resistor Divider
3-Resistor Divider
What Is a Voltage Divider?
A voltage divider is a resistor network that turns one input voltage into a smaller, predictable output voltage. Two resistors connect in series across a voltage source; the output is tapped from the point between them.
A 12V supply through a 1kΩ and 2kΩ resistor pair, for example, produces roughly 8V at the tap point. The ratio between the two resistor values sets exactly how much the voltage drops.
How Does a Voltage Divider Work?
Two resistors in series create a single voltage division point between them. Current flows through both resistors at the same rate, and each resistor drops a share of the total voltage proportional to its resistance.
The output voltage depends on two things: the resistor ratio (R2 relative to R1+R2) and the input voltage. Change either resistor and the output shifts; change the input voltage and the output scales with it, since the ratio stays fixed.
What Does a Voltage Divider Do?
A voltage divider scales a voltage down to a usable level, most often for one of four jobs: voltage scaling for measurement, sensor interfacing, analog input protection, or generating a stable reference voltage.
Microcontroller analog inputs, sensor circuits reading a variable resistance, and transistor bias networks all rely on the same basic division principle to turn one voltage into another, smaller, predictable one.
Voltage Divider Formula and Equation
Standard Voltage Divider Formula
The standard voltage divider formula is Vout = Vin × R2/(R1+R2). Vin is the source voltage in volts, R1 and R2 are the two series resistances in ohms (Ω), and Vout is the voltage measured at the node between them.
Once you calculate your output voltage and resistance values, you can use our main Ohm's Law Calculator (Homepage) to determine the total current draw and power consumption of your divider circuit.
R1 sits closest to the supply; R2 sits closest to ground. Vout always falls between 0V and Vin — a voltage divider can only reduce voltage, never increase it.
Voltage Divider Rule Explained
The voltage divider rule applies to resistors connected in series carrying the same current. Because the current through R1 and R2 is identical, the voltage drop across each resistor is directly proportional to its resistance relative to the total.
Use the divider rule whenever you need a fraction of a supply voltage and the circuit drawing current from the output is high-impedance (an ADC pin, an op-amp input) rather than a device that draws significant current of its own.
Voltage Divider Formula for Two Resistors
The most common voltage divider is a two-resistor series network: R1 from the supply to the output node, R2 from the output node to ground.
Example: Vin=12V, R1=1kΩ, R2=2kΩ → Vout = 8V
Divider current: 12V ÷ 3,000Ω = 4mA · Power: ~48mW total — well within a standard resistor's rating.
Voltage Divider With Multiple Resistors
A voltage divider can extend beyond two resistors — three, four, or more resistors in series each create their own tap points, with output voltage available at any node along the chain.
Total resistance is the sum of every resistor in the chain. The voltage dropped across any single resistor, or any combination measured to ground, follows the same ratio logic as the two-resistor case — just applied to a longer chain.
Voltage Divider With Three Resistors
For three resistors in series, the voltage at any tap point equals Vin times the resistance from that tap point down to ground, divided by the total resistance of the chain:
Example: with Vin = 12V, R1 = 1kΩ, R2 = 1kΩ, and R3 = 2kΩ, tapped at the node above R3, Rselected = R3 = 2,000Ω and Rtotal = 4,000Ω. Vout = 12 × 2,000/4,000 = 6V.
Voltage Divider Resistor Value Calculator
Choosing resistor values starts with the target ratio: pick any R1/R2 pair that produces Vout/Vin, then check two things before finalizing them.
Check the current draw first. Divider current is Vin/(R1+R2) — lower resistor values draw more current and dissipate more power; higher values draw less current but become more sensitive to loading from whatever reads the output.
Check available standard values second. Resistors come in fixed E-series values (E12, E24), not arbitrary numbers, so the practical approach is picking the closest standard pair to your ideal ratio and accepting a small, predictable error — usually well under 5% — rather than chasing an exact but unavailable value.
Voltage Divider Ratio Calculator
The divider ratio is Vout divided by Vin, and it's set entirely by R2/(R1+R2) — the same fraction that appears in the main formula, expressed as a standalone number instead of a voltage.
Example: scaling 5V down to 3.3V requires a ratio of 3.3/5 = 0.66. Any resistor pair where R2/(R1+R2) equals 0.66 produces that same 3.3V output, regardless of the actual resistance values chosen.
Common Voltage Conversion Reference Table
Voltage Divider for Arduino and Microcontrollers
Arduino analog input pins have a maximum voltage limit tied to their reference voltage, typically 5V on boards like the Uno. Feeding a higher voltage directly into an analog pin risks damaging the board.
A voltage divider scales a higher voltage — a 12V battery, for example — down into that safe range before it reaches the analog pin, so the board can measure a voltage far beyond what it could read directly.
Voltage Divider for ESP32
ESP32 analog-to-digital converter (ADC) pins typically read a maximum of around 3.3V, and ADC accuracy on many ESP32 boards degrades noticeably near both ends of that range — worth checking your specific board's datasheet before relying on readings close to 0V or 3.3V.
A voltage divider brings a higher voltage — battery voltage, a sensor output, a logic signal from a 5V system — down into the ESP32's safe input window for battery monitoring and general sensor measurement.
Voltage Divider Sensor Circuits
Sensors that change resistance in response to a physical condition — light, temperature, pressure — don't output a voltage directly. Placing one in a voltage divider converts that resistance change into a voltage change a microcontroller's analog input can read.
LDR / Photoresistor
Resistance drops as light increases. Output voltage rises or falls with ambient light — direct analog light-level reading.
Thermistor
Resistance shifts predictably with temperature. The voltage at the divider tap converts back to a temperature value using the thermistor's known curve.
Ultrasonic Sensor
Some modules output voltage above a microcontroller's safe input. A divider on the output line scales the signal down before it hits the input pin.
Voltage Divider With Potentiometer
A potentiometer is a voltage divider with an adjustable ratio. Using all three terminals — both ends plus the wiper — turns a fixed-value divider into one you can tune by hand, since moving the wiper changes the effective R1/R2 split in real time.
Common uses include volume controls, sensor calibration trimmers, and adjustable reference voltages — anywhere a fixed resistor pair would work, except the ratio needs to change during use rather than staying fixed at design time.
Voltage Divider With Capacitors
Capacitors can form a voltage divider in AC circuits using capacitive reactance instead of resistance. For two capacitors in series, the output voltage ratio is Vout = Vin × C1/(C1+C2) — notably the opposite relationship from resistors, since a capacitor's reactance decreases as its capacitance increases.
Resistor-capacitor combinations create frequency-dependent dividers rather than fixed ones — the output ratio changes with signal frequency, which is the basis of basic filter circuits rather than a simple fixed-ratio divider.
AC Voltage Divider Circuits
AC voltage division depends on impedance, not resistance alone. In a purely resistive AC divider, the standard formula still applies directly, since resistance doesn't change with frequency.
Once capacitors or inductors enter the circuit, reactance becomes frequency-dependent, and the division ratio shifts with the signal's frequency instead of staying fixed the way a pure resistor divider does.
Voltage Divider Bias Circuits
Voltage divider bias sets a stable, predictable base voltage for a bipolar junction transistor (BJT) or junction field-effect transistor (JFET), using two resistors from the supply to the transistor's base and from the base to ground.
This configuration holds the operating point steady despite normal variation in a transistor's current gain (beta) between individual components — a real weakness of simpler bias methods. It's the standard biasing approach in amplifier and switching circuit design.
Voltage Divider Applications
- Scaling battery or supply voltage for safe microcontroller measurement
- Reading resistive sensors (light, temperature, moisture) as an analog voltage
- Setting stable transistor bias points in amplifier circuits
- Shifting logic levels between 5V and 3.3V systems
- Creating reference voltages for comparators and analog circuits
- Attenuating audio signal levels between stages
Voltage Divider Limitations
No, a voltage divider is not an ideal voltage source. Its output voltage shifts under load, wastes power continuously even when idle, and depends on resistor accuracy for its precision — three real limitations worth knowing before using one in a design.
Voltage Divider Load Effect
Connecting a load resistor (RL) across the output changes the divider's effective ratio, because RL forms a parallel combination with R2 rather than leaving R2 isolated.
That parallel combination is always lower than R2 alone, which pulls Vout down from its unloaded, calculated value. The effect grows larger as the load resistance approaches the divider's own resistance values — a divider built from low resistor values resists loading better than one built from high resistor values, at the cost of drawing more continuous current.
Voltage Divider Accuracy and Resistor Tolerance
Real resistors carry a tolerance rating — commonly ±5% or ±1% — meaning the actual resistance can deviate from its printed value in either direction.
With two ±5% resistors in a divider, worst-case output error runs close to ±10%, since both resistors can deviate in opposite directions at the same time. Using ±1% precision resistors tightens that error to roughly ±2% worst case, which matters for reference voltages and precision sensor circuits where a few percent of error changes the reading meaningfully.
Voltage Divider vs Voltage Regulator
🏗 Voltage Divider
- Simple, passive — just two resistors
- Output shifts with load current
- Always draws current, even idle
- Best for signal scaling & sensing
⚡ Voltage Regulator
- Active component with feedback loop
- Holds output steady under load
- Corrects for input voltage fluctuation
- Best for powering real loads reliably
No, a voltage divider cannot regulate voltage the way a dedicated regulator can. A divider's output changes with load and drifts with resistor tolerance; it has no active mechanism correcting for either. Use a divider for low-current signal scaling and sensing; use a regulator whenever the output needs to power a real load reliably.
Voltage Divider and Ohm's Law Relationship
A voltage divider is a direct application of Ohm's Law to a series circuit. Since R1 and R2 carry the same current, that current equals I = Vin/(R1+R2) — Ohm's Law applied to the total series resistance.
The voltage across R2 is then Vout = I × R2, which is exactly Ohm's Law applied a second time, to R2 alone. Substituting the first equation into the second produces the divider formula: Vout = Vin × R2/(R1+R2). Kirchhoff's Voltage Law confirms the same result from a different angle — the voltage drops across R1 and R2 must sum to Vin, since there's nowhere else for that voltage to go in a single series loop.