Calculation
Vout = Vin · R2/(R1 + R2)
Vout = Vin·R2/(R1+R2); a connected load changes the ratio.
Kirchhoffsche Regeln
Voltage Divider Calculator
Vout = Vin·R2/(R1+R2); a connected load changes the ratio.
MINTSI
02
Result
Select a target and calculate.
Understand the inputs
- Output voltage Vout — The voltage that would be measured at the tap between R1 and R2 if no current is drawn there (unloaded divider). With a real load connected, this voltage sags a little.
- Input voltage Vin — The supply voltage applied across the whole series combination of R1 and R2. Source: the source's datasheet, or a measurement.
- Upper resistor R1 — The resistor between the input voltage Vin and the tap point (the output Vout).
- Lower resistor R2 — The resistor between the tap point and the reference potential (usually ground/0 V). The larger R2 is relative to R1, the higher the output voltage.
Example
12 V with 1 kΩ/(1.4 kΩ+1 kΩ) gives 5 V.
Assumptions and limits
Unloaded divider; source and load resistance are excluded.
Understand Voltage Divider Calculator
This calculator finds the missing quantity among output voltage Vout, input voltage Vin, and resistors R1 and R2 from the other two, for an unloaded voltage divider. It explains why a load connected at the output can pull the actual voltage below the calculated value.
What does this quantity describe?
A voltage divider made of two series resistors delivers a fraction of the input voltage at their junction: Vout = Vin·R2/(R1+R2). The ratio of R2 to the sum of both resistors sets what share of the input voltage appears at the output.
A potentiometer implements exactly this circuit mechanically: its wiper splits a single resistive track into two portions R1 and R2, whose ratio changes continuously as the control is turned — as in a volume knob.
Formula and variables
Vout = Vin · R2/(R1 + R2)
Vout = Vin · R2/(R1 + R2)Vin = Vout · (R1+R2)/R2R2 = R1 · Vout/(Vin − Vout)
| Symbol / input | Meaning |
|---|---|
| Output voltage Vout | The voltage that would be measured at the tap between R1 and R2 if no current is drawn there (unloaded divider). With a real load connected, this voltage sags a little. |
| Input voltage Vin | The supply voltage applied across the whole series combination of R1 and R2. Source: the source's datasheet, or a measurement. |
| Upper resistor R1 | The resistor between the input voltage Vin and the tap point (the output Vout). |
| Lower resistor R2 | The resistor between the tap point and the reference potential (usually ground/0 V). The larger R2 is relative to R1, the higher the output voltage. |
Choose the inputs correctly
Enter two of the four quantities. Vout requires Vin, R1 and R2 (or two of these together with Vout to find the fourth). The formula applies to an unloaded output with no connected load.
How to use the calculator
Select the target quantity and enter the other known values with units. For real use, plan a load resistance much larger than R1 and R2, so the calculated output voltage stays approximately valid under load.
Worked example
Given Vin = 12 V, R1 = 1,400 Ω and R2 = 1,000 Ω, substitution gives Vout = 12 V · 1,000/(1,400+1,000) = 5 V.
Understand the result and units
An output voltage of 5 V holds only as long as no load, or a very high-impedance one, is connected at the output. Once a real load draws current from the tap, actual voltage falls below this calculated value.
Voltage in volts (V), resistors in ohms (Ω) or kΩ. Since Vout depends only on the resistance ratio, R1 and R2 can use any unit as long as both are consistent.
How much does a connected load change the output voltage?
An unloaded voltage divider has an internal (Thévenin) resistance of Rth = R1·R2/(R1+R2). Connecting a load resistance RL at the output turns the divider and load into a second divider: Vout,loaded = Vout,unloaded · RL/(RL + Rth). If RL is much larger than Rth, the deviation stays small; if RL is comparable to or smaller than Rth, actual output voltage falls noticeably below the unloaded calculated value. In practice this is avoided with a high-impedance measurement input or a buffer amplifier (voltage follower).
Typical applications
Voltage dividers are used for level-shifting sensor and measurement signals, generating reference voltages, in potentiometers for volume and adjustment controls, and for rough voltage scaling in analog circuits.
Assumptions, limits and common mistakes
The formula applies to an unloaded divider with no current drawn at the output. A connected load resistance sits effectively in parallel with R2, lowering its effective value, so the real output voltage falls below the calculated value — the effect is strongest when the load is comparable in size to R1 and R2.
Common mistake: Do not neglect the loading effect: a low-impedance load at the output noticeably changes the effective divider voltage. A rule of thumb is that load resistance should be at least ten times R2 for the deviation to stay negligible; otherwise the calculation must be repeated using the parallel combination of R2 and the load.
Frequently asked questions
Why does the measured output voltage differ from the calculated value?
Usually the loading effect: a load or low-impedance meter connected at the output sits effectively in parallel with R2, pulling actual voltage below the unloaded calculated value.
How do I avoid the loading effect in practice?
Use a load resistance at least ten times R2, or buffer the output with a high-impedance amplifier input or a voltage follower.
How does a potentiometer work as a voltage divider?
A potentiometer's wiper mechanically splits a fixed total resistance into two portions R1 and R2, whose ratio changes continuously as it is adjusted, continuously varying the output voltage.