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Voltage Divider Calculator - Online Two Resistor Output Tool

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RL is in parallel with R2, affecting the actual output voltage.
COMMON PRESETS
Vin + R1 Vout R2 GND I
OUTPUT VOLTAGE (Vout)
5.00 V
Voltage Divider Ratio: 0.417
Divider Ratio 0.417 : 1
Current (I) 1.00 mA
Power @ R1 7.00 mW
Power @ R2 5.00 mW
Total Power 12.00 mW
Frequently Asked Questions

A voltage divider is a simple circuit that uses two resistors in series to produce a fraction of the input voltage. The output voltage is taken from the junction between the two resistors. The formula is Vout = Vin × R2 / (R1 + R2), where R1 is the resistor connected to Vin and R2 is connected to ground.

Consider these factors: (1) Current draw – smaller resistors increase current and power dissipation. (2) Load impedance – the load connected to Vout effectively parallels R2, altering the ratio. Choose R2 at least 10× smaller than the load for minimal loading effect. (3) Power rating – ensure each resistor's power rating exceeds the calculated dissipation. (4) Standard values – use E12/E24 series values for real-world applications.

This is usually due to load effect. Any device connected to Vout draws current and acts as a parallel resistance to R2, reducing the effective bottom resistance. Use the Load Resistance option in this calculator to model this. Also check resistor tolerances (±5%, ±1%, etc.) and multimeter input impedance.

Generally, no. Voltage dividers have poor load regulation — the output voltage drops significantly when current is drawn. They are best suited for signal-level applications (e.g., ADC inputs, reference voltages, sensor circuits) where very little current is needed. For power supply applications, use a voltage regulator (linear or switching) instead.

When you know the desired Vout but need to find the required resistor, use reverse mode. To find R2: R2 = R1 × Vout / (Vin − Vout). To find R1: R1 = R2 × (Vin − Vout) / Vout. Note that Vin must be greater than Vout for valid results.

Common uses include: ADC voltage scaling (e.g., 5V signal → 3.3V microcontroller input), biasing transistors in amplifier circuits, creating reference voltages, battery voltage monitoring, potentiometer circuits, and sensor interface circuits. They are fundamental building blocks in analog electronics.

A potentiometer is a variable voltage divider in a single package. It uses a resistive track with a sliding wiper, allowing you to adjust the division ratio continuously. Fixed-resistor dividers (like those calculated here) use two discrete resistors for a fixed ratio. Potentiometers are great for adjustable circuits, while fixed dividers are used when a stable, specific ratio is needed.

Resistor tolerance (±1%, ±5%, etc.) causes the actual Vout to vary from the calculated value. For critical applications, use ±1% or better tolerance resistors. You can estimate worst-case Vout by calculating with R1 at its maximum tolerance and R2 at its minimum (or vice versa). Many professional designs also include a small trim potentiometer for fine adjustment.
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