ToolForage.
ENERGY CALCULATOR

Voltage Divider Calculator

Calculate the output of a two-resistor DC divider, including an optional resistive load.

Calculator

V
Ω
Ω
Ω
Enter zero for no connected load. A positive value is placed in parallel with R2.
YOUR RESULTS
Loaded output voltage6 V
Unloaded output voltage
6 V
Supply current
0.0006 A
R1 dissipation
0.0036 W
R2 dissipation
0.0036 W

Page guide

Loaded divider voltage and resistor heating

The primary output includes the entered load. The unloaded result shows how much that load changes the nominal ratio. Resistor dissipation is calculated separately for R1 and R2; the connected load’s heating is not included in R2 power.

To check the parallel combination in the loaded bottom branch, the Parallel Resistor Calculator calculates equivalent resistance.

The formula

Unloaded Vout = Vin × R2/(R1 + R2). With load RL, Rbottom = R2 × RL/(R2 + RL), then Vout = Vin × Rbottom/(R1 + Rbottom).

A resistive output load is placed in parallel with the lower resistor. Its equivalent resistance reduces the divider ratio. Supply current flows through R1, while the lower branch current divides between R2 and the connected load.

Worked example

A 12 V source with two 10 kΩ resistors produces 6 V unloaded and draws 0.6 mA. Adding a 10 kΩ output load makes the bottom equivalent 5 kΩ; output becomes 4 V and source current 0.8 mA.

How to use this calculator

  1. Enter input voltage, upper resistor r1 using the units shown.
  2. Set lower resistor r2, output load resistance.
  3. Calculate and review loaded output voltage alongside the supporting quantities.

Zero means no external load in this form

A zero load input is a convenience for the unloaded calculation, not a physical zero-ohm short. A positive load value is modeled as a resistor from the output node to ground. The upper resistor runs from the supply to the output, and the lower resistor runs from output to ground. Reversing their positions changes the output.

Loading and source impedance

A divider is a resistive signal network, and its output can change when a device draws current. Real inputs may have leakage, capacitance, or dynamic current that a fixed load resistor does not represent. Component tolerance and supply impedance also affect voltage. This tool does not select preferred resistor values, an ADC protection circuit, or a regulated power supply.

Assumptions & limitations

What this calculation assumes

  • The supply is ideal DC and the optional load is purely resistive.

What to keep in mind

  • Excludes tolerances, dynamic input loading, capacitance, source impedance, and protection design.

Common questions

Why is the loaded voltage lower?

The load reduces the effective lower resistance by connecting in parallel with R2, changing the division ratio.

Can I power a device from this divider?

This model only calculates resistive loading. A changing device current will change the voltage; regulated power requirements need a suitable supply design.

What does the zero load setting mean?

It means no external load is connected in this form. It does not model a zero-ohm short circuit.

Sources & further reading

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