Voltage Divider Calculator
Enter the input voltage and the two resistor values to find the output voltage of a resistive divider, Vout = Vin x R2 / (R1 + R2), plus the current and ratio.
How to use the voltage divider calculator
- Enter the input voltage Vin in volts.
- Enter the top resistor R1 and the bottom resistor R2 in ohms.
- Read off the output voltage, the current and the divider ratio.
Examples
9 V across 1k and 2k
Vin = 9 V, R1 = 1000 ohm, R2 = 2000 ohm
Vout = 6 V, I = 3 mA, ratio = 0.667
Equal resistors halve the voltage
Vin = 5 V, R1 = 10000 ohm, R2 = 10000 ohm
Vout = 2.5 V
Frequently asked questions
What is the voltage divider formula?
For a divider where the output is taken across R2, Vout = Vin x R2 / (R1 + R2). The output is always a fraction of the input voltage.
How is the current found?
With no load on the output, the same current flows through both resistors: I = Vin / (R1 + R2), in amperes.
What does the ratio mean?
The ratio is Vout / Vin, equal to R2 / (R1 + R2). It tells you what fraction of the input appears at the output.
How do I pick R2 for a target output?
Rearranging the formula gives R2 = R1 x Vout / (Vin - Vout). This calculator can solve for R2 when you know Vin, Vout and R1.
Does this account for a load resistor?
No. It assumes an ideal, unloaded divider. A real load in parallel with R2 lowers the output voltage below the ideal value.
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