Voltage Divider Calculator
The output of a two-resistor voltage divider, or the resistor or input voltage that gives the output you need, with the current, the power in each resistor and an optional load.
Result
Output voltage, Vout: 3.836735 V
Ideal resistors and source. Real resistors are within their tolerance, so the output is too.
- Bottom resistor, R2
- 4.7 kΩ
- Top resistor, R1
- 10 kΩ
- Input voltage, Vin
- 12 V
- Current through R1
- 0.816327 mA (0.000816 A)
- Power in R1
- 0.006664 W
- Power in R2
- 0.003132 W
- Vout ÷ Vin
- 0.319728
https://calcgallery.com/electronics/voltage-divider-calculator/
Results come from the published equations applied to the values you enter. They are not electrical design, conductor sizing, laboratory safety or medical guidance. Weather indices describe a standard person in standard conditions and are not a forecast. Where codes apply, local rules vary and must be checked. Read the full disclaimer
How to use the Voltage Divider Calculator
- Choose what to find, the output voltage, one of the two resistors, or the input voltage.
- Enter the other three values, in volts or kilohms or whichever units suit.
- Optionally, under more options, enter the resistance of whatever the output feeds, to see how much it pulls the output down.
The formulas
Vout = Vin × R2 ÷ (R1 + R2)R2 = R1 × Vout ÷ (Vin − Vout)R1 = R2 × (Vin − Vout) ÷ VoutVin = Vout × (R1 + R2) ÷ R2with a load RL: R2 is replaced by R2 × RL ÷ (R2 + RL)The current through R1 is (Vin − Vout) ÷ R1, and the power in each resistor is the current squared times its resistance. Without a load the same current flows through both resistors.
Limits
The resistors are taken as exact and the source as having no resistance of its own. A load is only taken into account when solving for the output voltage; the resistor and input answers are for an unloaded divider. An output at or above the input is impossible for a divider, and the page says so rather than returning a negative resistance.
With your numbers
- Vout = Vin × R2 ÷ (R1 + R2) = 12 V × 4,700 Ω ÷ (10,000 Ω + 4,700 Ω) = 3.836735 V
Quick reference
Ideal resistors and source. Real resistors are within their tolerance, so the output is too.
| Example | Result |
|---|---|
| 12 V, 10 kΩ over 4.7 kΩ | Output voltage, Vout: 3.836735 V |
| 12 V, 10 kΩ over 4.7 kΩ, 10 kΩ load | Output voltage, Vout: 2.907216 V |
| 5 V, two equal resistors | Output voltage, Vout: 2.5 V |
| R2 for 5 V from 12 V, R1 10 kΩ | Bottom resistor, R2: 7.143 kΩ |
| R1 for 5 V from 12 V, R2 4.7 kΩ | Top resistor, R1: 6.58 kΩ |
| R2 for 3.3 V from 5 V, R1 10 kΩ | Bottom resistor, R2: 19.41 kΩ |
| Vin for 3.3 V over 10 kΩ and 20 kΩ | Input voltage, Vin: 4.95 V |
Common questions about the Voltage Divider Calculator
- How does a voltage divider work?
- Two resistors in series across a supply carry the same current, so the supply voltage splits between them in proportion to their resistances. The output is taken from the junction, across the bottom resistor: Vout = Vin × R2 ÷ (R1 + R2). With 10 kΩ over 4.7 kΩ on 12 V, the output is about 3.84 V.
- How do I choose R1 and R2 for a target voltage?
- Fix one resistor and solve for the other: R2 = R1 × Vout ÷ (Vin − Vout). For 5 V from 12 V with R1 at 10 kΩ, R2 is about 7.14 kΩ. The exact value is rarely a stock part, so pick a nearby preferred value and check the output it gives by solving for Vout.
- Why is the output lower when something is connected?
- The load sits in parallel with R2, and two resistances in parallel are lower than either alone, so the bottom of the divider shrinks and the output falls. A 10 kΩ load on the 10 kΩ over 4.7 kΩ divider drops 12 V to about 2.91 V instead of 3.84 V. Keeping the divider current well above the load current keeps the effect small.
- Can a divider power a circuit?
- Only one that draws very little and steadily, such as a sensor input or a reference pin. Because the output depends on the load, a divider cannot hold a voltage steady for a load that changes, and the resistors turn the supply current into heat. That is what a voltage regulator is for.