📉 Voltage Divider Calculator
Enter the input voltage and the two resistors to get the divider's output voltage, the current it draws and the power it dissipates.
Output voltage Vout
8 V
66.7% of Vin
Current through divider
4 mA
Power dissipated
48 mW
Vout = Vin × R2 ÷ (R1 + R2), measured across R2. This holds only when the load draws negligible current — for a real load, its resistance sits in parallel with R2 and lowers Vout, so use a buffer or a proper regulator for anything that draws power. 🔒 In your browser.
How the voltage divider calculator works
Two resistors in series split a voltage in proportion to their values. The output, taken across the lower resistor R2, is Vout = Vin × R2 ÷ (R1 + R2). The tool also gives the current flowing through the pair (Vin ÷ (R1 + R2)) and the power dissipated, so you can choose resistor values that don't waste too much energy.
This formula assumes the output feeds a high-impedance input (like an op-amp or ADC) that draws almost no current. A real load in parallel with R2 pulls the output down, so use lower resistor values relative to the load — or better, a buffer or regulator — when the output has to supply current.
Frequently asked questions
How does a voltage divider work?
Two resistors in series divide the input voltage. The voltage across the lower one (R2) is Vout = Vin × R2 ÷ (R1 + R2). Equal resistors give exactly half the input.
How do I calculate a voltage divider?
Vout = Vin × R2 ÷ (R1 + R2). For 12 V with R1 = 1 kΩ and R2 = 2 kΩ: 12 × 2000 ÷ 3000 = 8 V. Swap R1 and R2 to get the opposite ratio.
Can a voltage divider power a device?
Not really. As soon as the load draws current it upsets the ratio and the output sags, and dividers waste power as heat. Use them for reference/sense signals into high-impedance inputs; use a regulator to actually power something.
How do I pick resistor values for a divider?
Choose the ratio for the voltage you want, then scale the actual values: larger resistors waste less power but are more affected by loading and noise; smaller ones are stiffer but draw more current. A few kΩ to tens of kΩ suits most sensing.
What is the current through a voltage divider?
Vin ÷ (R1 + R2) when unloaded. For 12 V across 3 kΩ total that's 4 mA. The tool shows the current and the resulting power so you can keep dissipation reasonable.