What is the loading effect?

When a load is connected across R2, it draws current and reduces the output voltage. The load acts as a parallel resistor with R2, reducing the effective R2. For accurate output, the load impedance should be at least 10 times R2.

Can a voltage divider increase voltage?

No. A passive voltage divider can only reduce voltage. The output is always less than or equal to the input. To increase voltage, you need an active circuit like a boost converter or op-amp amplifier.

Why not just use one resistor to drop voltage?

A single resistor drops voltage proportionally to current (V = IR), but the voltage changes with load current. A voltage divider provides a more predictable output voltage, though it still has loading effects.

What resistor values should I choose?

Choose values large enough to minimize wasted current but small enough to drive the load. For signal conditioning, 1k-100k ohms is typical. For battery-powered circuits, higher values (100k-1M) reduce power waste.

How accurate is a voltage divider?

Accuracy depends on resistor tolerance and loading. With 1% tolerance resistors and light loading (load impedance greater than 100x R2), voltage dividers achieve better than 2% accuracy, sufficient for most applications.

Voltage Divider Calculator

Calculate output voltage of a resistive divider

Voltage Divider

Enter input voltage and resistor values

Input Voltage (V)

R1 (Ohms)

R2 (Ohms)

Formula

Vout = Vin x R2 / (R1 + R2)

What Is a Voltage Divider?

A voltage divider is one of the simplest and most widely used circuits in electronics. It uses two resistors connected in series to produce an output voltage that is a fraction of the input voltage. The output is taken from the junction between the two resistors, and its value depends on the ratio of the resistances.

Voltage dividers appear everywhere: in sensor circuits, reference voltage generators, level-shifting circuits, and potentiometer configurations. Understanding the voltage divider formula lets you set precise voltage levels without active components like op-amps or voltage regulators — often all you need is a pair of resistors.

How to Use This Calculator

Enter the input voltage (Vin) — the total supply voltage applied across both resistors.
Enter the value of R1 — the resistor connected between Vin and the output node.
Enter the value of R2 — the resistor connected between the output node and ground.
Click Calculate to see the output voltage (Vout) at the midpoint junction.

Formula & Explanation

Vout = Vin × (R2 / (R1 + R2))

Vin = input voltage, R1 = top resistor (Ω), R2 = bottom resistor (Ω), Vout = output voltage. The ratio R2/(R1+R2) is always between 0 and 1, so Vout is always less than Vin.

Worked Examples

Example 1 — Basic Divider

Vin = 12 V, R1 = 10 kΩ, R2 = 10 kΩ. Vout = 12 × (10 / (10 + 10)) = 12 × 0.5 = 6 V.

Example 2 — Unequal Resistors

Vin = 5 V, R1 = 30 kΩ, R2 = 10 kΩ. Vout = 5 × (10 / (30 + 10)) = 5 × 0.25 = 1.25 V.

Example 3 — 3.3 V from 5 V

To get 3.3 V from 5 V: R1 = 1.7 kΩ, R2 = 3.3 kΩ. Vout = 5 × (3.3 / (1.7 + 3.3)) = 5 × 0.66 = 3.3 V.

Frequently Asked Questions

Can a voltage divider power a load?▾

Technically yes, but voltage dividers are poor at powering loads. Adding a load resistor in parallel with R2 changes the effective resistance and shifts Vout. For load driving, use a voltage regulator instead.

Why does the load affect the output voltage?▾

The load appears in parallel with R2, reducing its effective resistance. This changes the divider ratio and lowers Vout. The effect is minimized when the load resistance is much larger than R2.

What is the output impedance of a voltage divider?▾

The Thevenin output impedance is R1 in parallel with R2 (R1||R2 = (R1×R2)/(R1+R2)). A lower output impedance makes the divider more stable against load variations.

Can I use a potentiometer as a voltage divider?▾

Yes — a potentiometer is essentially an adjustable voltage divider. The wiper position sets the ratio between the two resistance segments, giving a continuously variable output voltage.

What happens if R2 is zero?▾

If R2 = 0 Ω, Vout = 0 V regardless of Vin. If R1 = 0 Ω, the formula becomes undefined (division by zero), which in practice means Vout = Vin with a short circuit.