Calculation
R2L = R2∥RLUout = Uin·R2L/(R1+R2L)
The load is parallel to the lower resistor, reducing its effective value and the output voltage.
Busch 2006, Abschnitt 4.2.2.2
Loaded Voltage Divider Calculator
The load is parallel to the lower resistor, reducing its effective value and the output voltage.
MINTSI
02
Result
Select a target and calculate.
Output voltage of the loaded divider versus load resistance
The load sits in parallel with R₂ and pulls the output voltage down. Only when RL is much larger than R₂ (rule of thumb: at least ten times) does Uout approach the unloaded value (dashed). At RL = R₂ the drop is already substantial.
No curve point selected yet.
Understand the inputs
- Loaded output voltage Uout — Voltage at the tap after the connected load draws current from the lower divider branch.
- Input voltage Uin — Actual supply voltage applied across the complete divider.
- Upper resistor R1 — Resistance from supply to tap; it carries the combined load and lower-branch current.
- Lower resistor R2 — Divider resistor from tap to reference, connected in parallel with the load.
- Load resistance RL — Input resistance of the connected load between tap and reference.
Example
12 V, R1=1.2 kΩ, R2=1.0 kΩ and RL=2.2 kΩ give R2L=687.5 Ω and Uout≈4.37 V.
Assumptions and limits
Pure resistors and steady DC; source resistance, changing input current and component tolerances are excluded.
Understand Loaded Voltage Divider Calculator
This calculator shows the voltage a resistor divider actually delivers under load. It bridges the gap between the unloaded basic calculator and a tap connected to a sensor, ADC or device input that draws current.
What does this quantity describe?
Load resistance RL is electrically parallel to R2. First calculate R2L = R2·RL/(R2+RL), then use that equivalent resistance in the divider equation. The smaller RL is relative to R2, the further Uout falls.
Formula and variables
R2L = R2∥RLUout = Uin·R2L/(R1+R2L)
R2L = R2 · RL / (R2 + RL)Uout = Uin · R2L / (R1 + R2L)
| Symbol / input | Meaning |
|---|---|
| Loaded output voltage Uout | Voltage at the tap after the connected load draws current from the lower divider branch. |
| Input voltage Uin | Actual supply voltage applied across the complete divider. |
| Upper resistor R1 | Resistance from supply to tap; it carries the combined load and lower-branch current. |
| Lower resistor R2 | Divider resistor from tap to reference, connected in parallel with the load. |
| Load resistance RL | Input resistance of the connected load between tap and reference. |
Choose the inputs correctly
Measure Uin across the divider's outer terminals. R1 runs from supply to tap and R2 from tap to reference. RL is the effective input resistance connected across that same tap, obtained from a data sheet or measurement.
How to use the calculator
Enter the actual supply voltage, installed resistor values and the lowest expected RL. Calculate Uout and compare it with the connected circuit's permitted input thresholds.
Worked example
With Uin=12 V, R1=1.2 kΩ, R2=1.0 kΩ and RL=2.2 kΩ, R2L=687.5 Ω and Uout falls to about 4.37 V; unloaded it would be 5.45 V.
Understand the result and units
The difference from the unloaded value is loading error. If it is excessive, lower R1 and R2, increase RL, or buffer the tap with a voltage follower.
Resistances may be entered in Ω, kΩ or MΩ and are converted consistently. Uin and Uout use the same voltage dimension.
Typical applications
Useful for ADC inputs, meters, sensors, bias networks and any circuit whose input resistance is not much greater than R2.
Assumptions, limits and common mistakes
The model assumes linear resistors at steady state. Source resistance, dynamic input current, capacitors, protection diodes, self-heating and resistor tolerance are excluded.
Common mistake: Do not add RL in series: it is parallel to R2. For microcontroller inputs, a static data-sheet resistance may also be insufficient when a sampling capacitor draws brief current pulses.
Frequently asked questions
What is “Loaded voltage divider” used for?
Useful for ADC inputs, meters, sensors, bias networks and any circuit whose input resistance is not much greater than R2.
Where do the input values come from?
Measure Uin across the divider's outer terminals. R1 runs from supply to tap and R2 from tap to reference. RL is the effective input resistance connected across that same tap, obtained from a data sheet or measurement.
What does the result not cover?
The model assumes linear resistors at steady state. Source resistance, dynamic input current, capacitors, protection diodes, self-heating and resistor tolerance are excluded.