Part of Circuit and resistor calculators
Loaded Voltage Divider Calculator
See how a real load changes divider output voltage, current, and accuracy.
Inputs
Compare an ideal divider with the same divider connected to a finite load.
Results
A load comparable to R2 pulls the output downward. This matters for ADC inputs, bias networks, references, and any following stage with finite input resistance.
Use the loaded divider check whenever Vout drives a real input
An ideal divider assumes no output current is drawn. Real ADC inputs, bias networks, references, enable pins, measurement instruments, and following stages can present finite resistance and change the divider output.
ADC and sense inputs
Check whether the divider is stiff enough before using the result as a measurement input.
Bias networks
Check output movement when another resistor network is connected to the divider node.
High-value dividers
Large divider resistors save current but are more sensitive to leakage, bias current, and loading.
Equations and practical model
The loaded divider model replaces the bottom resistor with the parallel combination of R2 and the load, then recalculates the divider output.
Ideal divider output
The unloaded output before the following circuit is connected.
Loaded lower leg
The load resistance appears in parallel with the bottom divider resistor.
Loaded output
The actual output after the load changes the lower-leg resistance.
Rload - Load resistance
Unit: ohms (Ω)
The resistance presented by the following input, bias network, or measurement circuit.
Req - Equivalent lower resistance
Unit: ohms (Ω)
R2 in parallel with the load resistance.
Iload - Load current
Unit: amps (A)
Current drawn by the following circuit from the divider output node.
Error - Loading error
Unit: percent (%)
How far the loaded output falls below the ideal unloaded output.
Worked example
The example below is checked against the shared loaded-divider calculation helper used by the calculator.
Design question: A 5 V divider uses R1 = 10 kΩ and R2 = 10 kΩ. What happens when it drives a 10 kΩ load?
Ideal output: Videal = 5 V × 10 kΩ / (10 kΩ + 10 kΩ) = 2.5 V.
Loaded lower leg: R2 ∥ Rload = 10 kΩ ∥ 10 kΩ = 5 kΩ.
Loaded output: Vloaded = 5 V × 5 kΩ / (10 kΩ + 5 kΩ) = 1.667 V.
Loading error: the output falls by about 33.3% compared with the ideal value.
Load current: Iload = 1.667 V / 10 kΩ = 166.7 µA.
Equivalent resistance and Thevenin view
A voltage divider can be viewed as a source with an output resistance. The connected load forms another divider with that output resistance, which is why high-value dividers are easy to disturb.
At the output node
- The ideal output is the open-circuit voltage.
- The divider output resistance is R1 in parallel with R2.
- A finite load makes another divider with that output resistance.
Design implication
- Lower divider resistance gives a stiffer output but wastes more current.
- Higher divider resistance saves current but increases loading error.
- Buffers or different resistor values may be needed when the error is too high.
Assumptions and limitations
Static load model
The load is treated as a fixed resistance. Switched, sampled, or capacitive inputs need extra timing analysis.
No tolerance corners
The calculator shows nominal error. Resistor tolerance, leakage, bias current, and input-voltage variation can move the result further.
Not an ADC settling check
ADC inputs can also require source-impedance and acquisition-time checks that are not captured by a DC resistance model.
Related calculators and next checks
Follow the next check based on whether the problem is ideal ratio, power, tolerance, or a following input that needs a better model.
Voltage divider calculator
Start here for the ideal divider ratio, divider current, and resistor power.
Resistor power calculator
Check divider resistor wattage once current and voltage drops are known.
Ohm's Law calculator
Sanity-check branch current, voltage drop, and equivalent resistance values.
Ideal vs loaded divider guide
Review why the unloaded divider equation can mislead real circuit design.
Divider tolerance guide
Add resistor tolerance and worst-case output movement after checking load error.
Circuit and resistor hub
Follow the surrounding resistor and interface workflows.
FAQ
Why does the load usually pull the divider output down?
The load resistance is effectively in parallel with R2. That makes the lower leg smaller, so the divider ratio decreases and the output voltage falls below the ideal unloaded value.
What load resistance is high enough?
There is no universal value. If the load resistance is much larger than the divider output resistance, the error may be small. For real design work, calculate the error instead of relying on a fixed rule.
Is an ADC input just a resistance?
Not always. Some ADC inputs are dynamic loads because of sampling capacitors and acquisition timing. This calculator is a static resistance model, so fast or high-impedance ADC inputs may need a settling-time check too.
Engineering reference
Equations, assumptions, and design guidance
Models an ideal DC voltage divider with a finite resistive load in parallel with the lower divider resistor.
Equations and variables
Req = R2 || RloadVout = Vin * Req / (R1 + Req)error = (Videal - Vout) / Videal- Vin
- Input voltage (V)
- R1
- Top resistor (ohm)
- R2
- Bottom resistor (ohm)
- Rload
- Load resistance (ohm)
Assumptions and limitations
Assumptions
- The load is resistive and static.
- The source is ideal and DC.
- Resistors are nominal values.
Limitations
- Input bias current, ADC sampling capacitance, leakage, and resistor tolerance are not included here.
- Use the voltage-divider set-point workflow for tolerance-aware preferred-value selection.
Worked example and design use
10 k / 10 k divider loaded by 100 k
Inputs: Vin = 5 V, R1 = 10 kOhm, R2 = 10 kOhm, Rload = 100 kOhm
Outputs: Loaded output is lower than the ideal 2.5 V result, R2 || Rload is reported for loading review
Design guidance
- Keep the load resistance much larger than the divider Thevenin resistance when the divider ratio must remain accurate.
- Check loaded divider current against source and power budget limits.