# Voltage Divider Calculator

Calculate voltage divider output, current, and power dissipation. Enter input voltage, R1, and R2 for instant results. Free online electronics calculator.

## What this calculates

A voltage divider uses two series resistors to produce an output voltage that is a fraction of the input voltage. The output voltage is Vout = Vin x R2 / (R1 + R2). This calculator also computes the current through the divider and power dissipated by each resistor.

## Inputs

- **Input Voltage** (V) — min 0 — Supply voltage applied across both resistors.
- **R1 (Top Resistor)** (Ω) — min 0.01 — Resistance of the top resistor connected to the input voltage.
- **R2 (Bottom Resistor)** (Ω) — min 0.01 — Resistance of the bottom resistor connected to ground.

## Outputs

- **Output Voltage** (V) — Voltage across R2 (Vout = Vin × R2 / (R1 + R2)).
- **Current** (mA) — Current flowing through the divider.
- **Power Dissipated (R1)** (mW) — Power dissipated by the top resistor.
- **Power Dissipated (R2)** (mW) — Power dissipated by the bottom resistor.
- **Total Power Dissipated** (mW) — Total power dissipated by the voltage divider.

## Details

The voltage divider is one of the most fundamental circuits in electronics. It consists of two resistors in series connected across a voltage source. The output is taken across the bottom resistor (R2). The formula Vout = Vin × R2 / (R1 + R2) assumes negligible load current.

Voltage dividers are used to scale down voltages for measurement by ADCs, create reference voltages, and bias transistors and op-amps. For example, to read a 12V battery with a 3.3V microcontroller ADC, you would use a divider that scales the voltage by 3.3/12.

An important limitation is that voltage dividers are load-sensitive. If a load draws significant current from the output, it effectively parallels R2, reducing the output voltage. For this reason, voltage dividers work best when the load impedance is at least 10 times greater than R2. For heavy loads, use a voltage regulator instead.

## Frequently Asked Questions

**Q: What is a voltage divider used for?**

A: Voltage dividers are used to reduce voltage levels, create reference voltages, bias transistors, interface sensors with microcontrollers, and scale down signals for measurement.

**Q: Does a voltage divider waste power?**

A: Yes. Current flows through both resistors continuously, dissipating power as heat. The total power is P = V²/(R1+R2). Use higher resistance values to minimize power waste, but ensure the divider can still drive the load.

**Q: Why does loading affect the voltage divider output?**

A: A load in parallel with R2 reduces the effective bottom resistance, shifting the divider ratio and lowering the output voltage. This effect is negligible when load impedance is much larger than R2.

**Q: Can I use a voltage divider instead of a voltage regulator?**

A: Only for very light loads. Voltage dividers cannot maintain a stable output under varying load currents. For stable, regulated voltage, use a linear regulator or switching regulator.

---

Source: https://vastcalc.com/calculators/technology/voltage-divider
Category: Technology
Last updated: 2026-04-21