Tool · Circuit fundamentals
Voltage Divider Calculator
Calculate the output of a two-resistor divider, see how a load changes it, and follow the reasoning behind the result.
Calculate
Inputs
Calculate
Results
With load connected
The load significantly changes the divider output. This is an educational warning threshold, not a universal engineering limit.
Visualize
See the circuit relationship.
The output node is shared by the lower resistor and, when enabled, the load.
Understand
How the calculation works
Unloaded divider
Vout = Vin × R2 / (R1 + R2)5 V × 20 kΩ / (10 kΩ + 20 kΩ) = 3.333 V
Loaded divider
Req = R2 || RLReq = 20 kΩ || 20 kΩ = 10 kΩ
Vout_loaded = Vin × Req / (R1 + Req)5 V × 10 kΩ / (10 kΩ + 10 kΩ) = 2.5 V
What changes what?
R2 increases → Vout tends to increase.
R1 increases → Vout tends to decrease.
Load resistance becomes smaller → loading becomes stronger → Vout decreases.
Apply
Engineering interpretation
Voltage dividers are useful for reference or signal voltages when the load is sufficiently high impedance.
A resistor divider is generally not a substitute for a regulated power supply when meaningful load current is required.
ADC and input circuits can load a divider depending on input impedance and sampling behavior.
Real resistor tolerances affect the actual output voltage, so verify the design against component specifications and circuit conditions.