Voltage Divider Calculator

With the output taken across R2, Vout = Vin x R2 / (R1 + R2). The current is I = Vin / (R1 + R2) and the ratio is R2 / (R1 + R2). All three follow from Ohm's law for two series resistors.

Switch the Mode dropdown to Find R2 for a target Vout. The tool rearranges the formula to R2 = R1 x Vout / (Vin - Vout) and shows the Required R2 in ohms.

This is an unloaded, ideal divider. Any load connected across R2 sits in parallel with it, lowering the effective bottom resistance and pulling the output below the calculated value. Keep the load resistance well above R2, or add a buffer, to stay close to the ideal figure.

No. A resistive divider only attenuates, so Vout always lands between 0 and Vin. In R2 mode the tool rejects any target Vout that is equal to or greater than Vin.

The engine guards against a zero total: if R1 + R2 is zero it reports an error instead of dividing by zero. A single resistor may be zero on its own as long as the pair sums above zero.

No. Voltage and resistance are treated as non-negative, and the calculator flags negative entries rather than returning a meaningless result.

Vout is in volts, the current is in amperes, and the ratio is a pure number with no unit. To read small currents as milliamps, multiply by 1000; 0.003 A is 3 mA.

The Current card shows I = Vin / (R1 + R2), the quiescent current flowing through the pair with no load. Larger resistor values cut this current and save power but make the output more sensitive to loading.

No. Every calculation happens locally in your browser with plain JavaScript, so your voltages and resistor values never leave your device.