Voltage Divider Calculator
Calculate the output voltage of a resistor divider, with or without a load.
About the Voltage Divider Calculator
Enter the input voltage, the top and bottom resistors and, if something is connected to the output, its resistance. The calculator gives the output voltage, the current through the divider and the division ratio.
Two resistors in series split the input voltage in proportion to their values. A load connected across R2 is in parallel with it and pulls the output down unless the load is much larger than R2 (at least 10×).
The formula
Vout = Vin × R2 ÷ (R1 + R2)
Worked example
12 V with R1 = 10 kΩ and R2 = 4.7 kΩ
- Vout = 12 × 4.7 ÷ 14.7 = 3.84 V
- With a 10 kΩ load on the output: 2.91 V
- The load is only about 2× R2, so it drags the output down
Questions people ask
Can I power a device from a divider?
Usually not; use a regulator. Dividers suit sensing and reference voltages.
How do I pick values?
Choose the ratio, then values that keep current small but much lower than the load.
How do I read 12 V with a 3.3 V microcontroller?
Use a ratio below 0.275, such as 10 kΩ over 3.3 kΩ, which gives about 2.98 V.