Voltage Divider Calculator

Voltage divider: scaling Vin with two resistors

A voltage divider uses two resistors in series to produce an output voltage that is a fraction of the input: Vout = Vin · R₂ / (R₁ + R₂), measured across R₂. Example: V_in = 5 V with R₁ = R₂ = 10 kΩ gives V_out = 2.5 V. The divider current is I = V_in / (R₁ + R₂), and total power is P = V_in · I. Critical limitation: a bare divider (no op-amp buffer) is loaded by the next stage — any current pulled from V_out changes the output voltage. Rule of thumb: the divider current should be at least 10× the load current to keep V_out "stiff". For high-impedance loads use a unity-gain op-amp (voltage follower) after the divider.

Applications: sensors, logic level shifting, references

Voltage dividers read resistive sensors (LDR, NTC, potentiometer) into an MCU analog input (0–5 V on Arduino, 0–3.3 V on ESP32). They shift logic levels down — for example, scaling a 5 V Arduino TX to 3.3 V for an ESP32 RX using R₁ = 1 kΩ, R₂ = 2 kΩ. They also create simple voltage references and biasing networks in amplifier stages.

FAQ

Why does my V_out drop when I connect a load? The load is in parallel with R₂, lowering the effective bottom resistance and shifting the ratio. Either use lower-value resistors (more divider current) or buffer with an op-amp.

Can I use it to power a circuit? Only for very low-current loads (microamps). For real power use a regulator (LDO, buck converter), not a divider.

What resistor values should I pick? Trade-off: small values waste power (high quiescent current), large values are sensitive to loading and noise. For MCU sensor reads, 1–100 kΩ is typical.