Calculators
Voltage Divider Calculator
Find the output voltage, R1, or R2 of a two-resistor voltage divider with Vout = Vin × R2 / (R1 + R2), plus divider current and resistor power, locally in your browser.
A voltage divider uses two resistors in series to produce a lower output voltage from a larger input. Choose what to solve for, then enter the other values. Voltages are in volts and resistances are in ohms. The result also reports the divider current and the power dissipated in each resistor. Calculations run locally in your browser; your values are not uploaded or stored.
Solve Vout = Vin × R2 / (R1 + R2) for the output or either resistor.
A voltage divider places two resistors in series and takes the output across the bottom resistor, so Vout is a fixed fraction of Vin set by R2 / (R1 + R2). Choose what to solve for, then enter the other values: voltages in volts and resistances in ohms. For example, 12 V across R1 = 1000 ohms and R2 = 1000 ohms gives Vout = 12 × 1000 / (1000 + 1000) = 6 V, a divider current of 6 mA, and about 36 mW dissipated in each resistor. To solve for R1 enter Vin, Vout, and R2, and to solve for R2 enter Vin, Vout, and R1. The output voltage must be greater than zero and less than the input voltage for a passive divider, and every input must be positive. The result reports the divider current in amps and milliamps and the power in watts and milliwatts. This is an electronics estimate that assumes ideal resistors and no load on the output; all calculations stay in your browser.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
Which formula does the voltage divider calculator use?
It uses the two-resistor divider equation Vout = Vin x R2 / (R1 + R2), where Vin is the input voltage, R1 is the top resistor, R2 is the bottom resistor, and Vout is the output taken across R2. Rearranged, R1 = R2 x (Vin - Vout) / Vout and R2 = R1 x Vout / (Vin - Vout).
Which units should I use?
Enter voltages in volts and resistances in ohms. The result reports the divider current in amps and milliamps and the power in watts and milliwatts. You can enter any consistent voltage unit and resistance unit, as long as both voltages share one unit and both resistances share the other.
Why must the output voltage be less than the input voltage?
A passive divider made from two positive resistors can only attenuate, so Vout is always smaller than Vin. When solving for R1 or R2 the calculator requires Vout to be greater than zero and less than Vin; otherwise the result would need a negative resistance, which has no physical meaning here.
What do the current and power results mean?
Both resistors carry the same divider current, equal to Vin / (R1 + R2) when solving for Vout, or Vout / R2 when solving for a resistor. The power in each resistor is I squared times its resistance. Keep those values within each resistor wattage rating so it does not overheat.
Is this a substitute for a circuit simulator?
No. It applies the ideal divider equation and assumes no load on the output and ideal resistors. A real load in parallel with R2 lowers Vout and resistor tolerances shift the ratio. Use it as a quick estimate and verify with a simulator or measurement for critical designs. The calculation and copy run locally in your browser; CodeASystem does not upload or store your values.