Voltage Divider Calculator
Two resistors in series are the simplest way to step a voltage down: tap the point between them and the output is the input scaled by the bottom resistor's share of the pair. The formula is Vout = Vin × R2 / (R1 + R2), where R1 sits between the input and the tap and R2 between the tap and ground.
Enter the input voltage and both resistors in ohms to get the output voltage, the divider ratio, the current the pair draws and the total resistance, with the formula worked through using your numbers.
The two dividers everyone needs: 3.3 V from 5 V (R1 10 kΩ over R2 20 kΩ gives 3.33 V) and 5 V from 12 V (R1 14 kΩ over R2 10 kΩ, the exact 7 : 5 ratio, gives exactly 5 V).
Result
Vout = Vin × R2 / (R1 + R2) = 5 V × 20 kΩ / (10 kΩ + 20 kΩ) = 3.33 V
I = Vin / (R1 + R2) = 5 V / 30 kΩ = 0.167 mA
| Quantity | Value |
|---|---|
| Output voltage Vout | 3.33 V |
| Divider ratio Vout/Vin | 0.667 (66.7 %) |
| Current draw | 0.167 mA |
| Total resistance R1 + R2 | 30 kΩ |
R1 sits between the input and the tap, R2 between the tap and ground. The output is a fixed fraction of the input, and it holds only while the load draws less than about a tenth of the divider's own current. With 5% tolerance parts the real output lands within a few percent of the figure shown.
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