Unloaded divider
V_out = V_in R₂/(R₁+R₂)
The standard ideal two-resistor divider relationship.
Voltage Divider Calculator
Compare an ideal unloaded resistor divider with the same divider after a finite load is connected across the bottom resistor.
Access: Free to use, no installation, and No account required.
Inputs
Set load resistance to 0 for the unloaded case. The model assumes ideal resistors and a zero-impedance voltage source.
Results
Loaded divider behavior
A finite load appears in parallel with the bottom resistor. That reduces the effective lower resistance and usually pulls the output below the unloaded divider voltage.
Engineering reference
Voltage Divider Calculator: background and worked detail
Use the Voltage Divider Calculator to compare unloaded and loaded divider output voltage, source current, load current, effective lower-leg resistance, and loading error for two resistors with an optional finite load.
The divider ratio
Loaded lower resistance
R_eq = R₂ ∥ R_L
The load appears in parallel with the lower divider resistor.
Loaded output
V_out,loaded = V_in R_eq/(R₁+R_eq)
Loading lowers the effective bottom resistance and changes the ratio.
Loading is the usual surprise
An unloaded two-resistor divider sets output voltage by the ratio R2/(R1+R2). A finite load connected to the output appears in parallel with R2, reducing the effective lower resistance and usually pulling the output below the unloaded value.
The calculator is useful for understanding loading, but high-impedance sensor nodes, ADC inputs, bias networks, and dynamic circuits may also require source impedance, leakage, capacitance, noise, and settling-time analysis.
5 V divider with 10 kΩ / 10 kΩ and 100 kΩ load
Use Vin = 5 V, R1 = 10 kΩ, R2 = 10 kΩ, and RL = 100 kΩ.
- The unloaded output is 2.50 V.
- R2 ∥ RL is about 9.09 kΩ.
- The loaded output is about 2.381 V, a reduction of about 4.76% from the unloaded result.
Result: The example shows why a load only ten times larger than R2 can still create noticeable divider error.
Assumptions and model boundaries
Assumptions
- Resistors and load are ideal, linear, and time-invariant.
- The output load is modeled as a pure resistance.
- The source is treated as an ideal voltage source.
Limitations
- Does not model ADC sampling capacitors, input leakage, frequency-dependent loads, resistor tolerance/noise, or source impedance.
- Not suitable by itself for precision reference design without error budgeting.
Validation checks
Open-circuit load
Case: Use a very large load resistance.
Expected: Loaded output should approach the unloaded divider voltage.
Equal divider
Case: Set R1 = R2 with no meaningful loading.
Expected: Output should approach one half of input voltage.
Voltage Divider Calculator FAQ
How large should the load resistance be?
A common goal is to make the load much larger than the divider's Thevenin resistance, but the acceptable ratio depends on the allowed voltage error.
Why is the output lower when loaded?
The load is in parallel with the lower resistor, so the effective lower resistance decreases and changes the divider ratio.
Can a voltage divider power a large load?
Usually not efficiently. Dividers are best for signal and bias scaling; power loads generally need a regulator or power-conversion stage.
Where this calculation comes from
Shared with the Introductory Circuits Workbench, which models source and load impedance explicitly.
Open the source workbench →Read calculation and source methodology →