Voltage Divider Calculator

The Voltage Divider Calculator computes the output voltage of a resistive voltage divider network — one of the most frequently used circuit configurations in hobby electronics. The voltage divider is a simple two-resistor circuit that produces a fraction of its input voltage at the output node between the two resistors. It appears in analog signal conditioning, sensor interfacing, ADC input scaling, bias networks, and countless other applications in Arduino and maker projects.

The formula is elegantly simple: Vout = Vin × R2 / (R1 + R2). R1 sits between the input voltage and the output node; R2 sits between the output node and ground. The output voltage is determined entirely by the ratio of R2 to the total resistance. If R1 equals R2, the output is exactly half the input. If R2 is much larger than R1, the output approaches the input voltage. If R1 is much larger than R2, the output approaches zero.

One of the most common maker applications is level shifting — converting a higher logic voltage to a lower one for microcontroller input pins. For example, many sensors output 5V signals, but ESP32 and Raspberry Pi GPIO pins are only 3.3V tolerant. A properly designed voltage divider scales 5V down to 3.3V (using R1 = 10kΩ and R2 ≈ 20kΩ). This protects the 3.3V GPIO from damage while maintaining correct logic levels. This is far simpler and cheaper than a dedicated level-shifter IC for signal-only (non-bidirectional) applications.

Another important application is battery voltage monitoring with a microcontroller ADC. A fully charged 12V battery exceeds the 3.3V or 5V ADC input range. A voltage divider scales the 12V range down proportionally — using R1 = 100kΩ and R2 = 20kΩ gives Vout = 12 × 20 / 120 = 2.0V, which is safely within ADC range. The ADC reading is then multiplied by the inverse ratio (120/20 = 6) to recover the actual battery voltage in software.

Voltage dividers are also used to set the reference voltage for operational amplifiers, create bias points for transistor circuits, generate mid-rail references for single-supply audio circuits, and set threshold voltages for comparator circuits. Understanding the voltage divider is therefore a prerequisite for understanding a large fraction of analog circuit design.

The critical limitation of the voltage divider is that it is not a regulated voltage source. The output voltage is valid only when the load impedance is much larger than R2 (at least 10× larger). When a load draws current from the output node, it appears in parallel with R2, lowering the effective R2 and thus the output voltage. This effect is called loading. For sensor interfacing into a high-impedance ADC input (typically 100kΩ–1MΩ), loading is negligible with 10kΩ resistors. For driving lower-impedance loads, a voltage regulator or op-amp buffer is needed.

Power consumption is also an important consideration for battery-powered projects. The quiescent current flows continuously through both resistors even when no measurement is occurring. Using 100kΩ resistors instead of 10kΩ reduces quiescent current by 10× with no change in voltage ratio — critical for battery life in IoT nodes. This calculator shows both quiescent current and total power dissipation so you can make informed decisions about resistor sizing for your power budget.