Free tool · Electronics
Voltage Divider Calculator
Enter an input voltage and two resistor values to find the output voltage a divider produces, and the current flowing through it.
The formula
Two resistors in series carry the same current, so the voltage across each is proportional to its resistance. The output, taken across R2, is:
R1 sits between Vin and the output node; R2 sits between the output node and ground.
The current flowing through both resistors follows directly from Ohm's law applied to the pair in series:
The full input voltage is dropped across the total resistance R1 + R2.
Worked example
A 9 V supply feeds a divider made of R1 = 1 kΩ and R2 = 2 kΩ.
Substitute Vin, R1 and R2 directly into the divider formula.
The same current flows through both resistors.
Frequently asked questions
What is a voltage divider used for?
Two resistors in series split a supply voltage into a smaller, known fraction of it — used to scale a sensor's output into a microcontroller's input range, set a reference voltage, or bias a transistor. It's one of the most common two-component circuits in electronics.
Which resistor is R1 and which is R2?
R1 is the resistor between the input voltage and the output node; R2 is the resistor between the output node and ground. Vout is always taken across R2 — swapping the labels swaps which fraction of Vin you get out.
Does a voltage divider still work if I connect a load to the output?
Only approximately. This calculator assumes nothing draws current from the output node. If you connect a load, it effectively sits in parallel with R2, pulling the output voltage down — the lower the load's resistance compared with R2, the bigger the error.
How do I choose sensible resistor values for a divider?
Pick values large enough that the divider doesn't waste much current or power, but small enough that any load connected to the output doesn't disturb the voltage significantly. A few kΩ to a few tens of kΩ is a common range for low-power sensor and logic circuits.
What's the difference between a voltage divider and a potentiometer?
They're the same principle: a potentiometer is a single variable resistor with three terminals, wired as a divider whose R1:R2 ratio you can adjust with a dial or slider, instead of two fixed resistors.
Can a voltage divider power a circuit directly?
Not reliably. Because its output voltage depends on the load drawing negligible current, a divider is suited to feeding a high-impedance input (like an ADC pin), not supplying meaningful current to a load — for that, use a proper voltage regulator.
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