Electronics / Circuits

Voltage Divider Calculator

Calculate output voltage, current, and power dissipation for a resistive voltage divider — either a simple two-resistor pair or a longer series chain — and design a divider for a target output voltage.

Voltage divider Ohm's law Resistors in series Power dissipation
Results Real-time

Circuit Diagram

Output Voltage
—
V
Current
—
A
P (R1)
—
W
P (R2)
—
W
Total Power
—
W

Vout vs. R2 (operating point highlighted)

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About This Simulator

A voltage divider is one of the most fundamental circuits in electronics: two or more resistors connected in series across a voltage source, with an output tap taken between them. Because the same current flows through every resistor in the chain, the voltage source splits proportionally across each resistor according to Ohm's law (V = IR). This simulator covers two cases — a simple two-resistor divider and a longer N-resistor series chain — and computes the output voltage, the circuit current, and the power each resistor must dissipate.

Voltage dividers are used constantly in real designs: scaling a sensor signal down to fit a microcontroller's ADC range, setting a reference voltage, biasing a transistor, or building a simple potentiometer-style control. The trade-off is always the same — lower resistances draw more current and dissipate more power, while higher resistances are more sensitive to loading effects from whatever is connected to the output tap.

How to Use

  1. Choose a mode. "Two-Resistor" models the classic R1/R2 divider; "Series Chain" lets you add up to 8 resistors and taps the output across the last one.
  2. Enter the input voltage (Vin) and the resistor values. In series-chain mode, use "+ Add resistor" and the trash icon to build the chain.
  3. Optional — Design mode. In two-resistor mode, flip the "Design mode" switch, enter a target Vout, and pick which resistor is fixed. The other resistor is solved for automatically.
  4. Read the results on the right: a circuit diagram of your current configuration, output voltage, current, and power dissipation per resistor. Values that exceed a standard 0.25 W (1/4 W) resistor rating are flagged, both in the results and in the diagram's tap and chart colors.

Understanding the Results

Output Voltage (Vout)

The voltage measured at the tap point. In the two-resistor case, Vout = Vin × R2 / (R1 + R2). In the series-chain case, Vout is the voltage across the last resistor in the chain relative to ground.

Current

The single current that flows through every resistor in the divider, I = Vin / Rtotal. This assumes an ideal, unloaded output — connecting a load at the tap will draw additional current and pull Vout down (loading effect), which this simulator does not model.

Power Dissipation

Each resistor dissipates P = I²R as heat. The simulator flags any resistor whose dissipation exceeds 0.25 W, the typical rating of a small through-hole resistor — a useful reminder to size resistors (and their wattage rating) appropriately, especially with low resistances or high input voltages.

Frequently Asked Questions

Why is my actual output voltage lower than calculated?
This calculator assumes an unloaded (ideal) output. If you connect anything to the tap point — a microcontroller pin, a meter with finite input impedance, another circuit — it draws current and effectively adds a resistor in parallel with the lower leg, which pulls Vout down. This is called the "loading effect." To minimize it, use resistor values much smaller than the load's input impedance, at the cost of higher power dissipation.
What does Design mode actually solve for?
Design mode rearranges the divider equation to solve for the resistor you are not fixing, given Vin and a target Vout. If R1 is fixed, R2 = R1 × Vout / (Vin − Vout); if R2 is fixed, R1 = R2 × (Vin − Vout) / Vout. It still assumes an ideal, unloaded output — see the note on loading effects above.
How is Vout defined in Series Chain mode?
Vout is always measured across the last resistor you add (closest to ground). The per-resistor breakdown table shows the individual voltage drop and power dissipation across every resistor in the chain, which is useful if you need the voltage at an intermediate node — just look at the cumulative drop up to that point.
What are the limitations of this simulator?
It models an ideal, unloaded, DC-only divider with perfect resistor values — it does not account for load impedance, resistor tolerance, temperature drift, or AC effects like parasitic capacitance. The 0.25 W overload warning is a rule-of-thumb flag for a small through-hole resistor, not a substitute for checking the actual datasheet rating of the parts you plan to use.