Voltage Divider Calculator

Voltage Divider Tool

Input Voltage (Vin)

Resistor Unit

Top Resistor (R1)

Connected from Vin to Vout.

Bottom Resistor (R2)

Connected from Vout to ground.

Optional Load Resistor (RL)

When set, RL is in parallel with R2 to compute loaded output voltage.

Quick Divider Ratios (uses R2 = 10)

Unloaded Output (Vout)

0 V

Loaded Output (with RL)

0 V

Voltage Drop Distribution

R1 drop: 6.00 V R2/RL node: 6.00 V

Divider Current

0 A

R2||RL Effective

Attenuation (Loaded)

Power in R1

0 W

Power in R2

0 W

Power in RL

How It Works

A voltage divider is one of the most common analog building blocks in electronics. It lets you scale a source voltage down to a lower level using two resistors. This is useful for sensor interfacing, ADC inputs, biasing transistor stages, and creating reference voltages.

Unloaded: Vout = Vin * (R2 / (R1 + R2))

In the ideal unloaded case, only R1 and R2 matter. Real circuits usually attach some load to the output node, and that load acts in parallel with R2. The effective lower resistance becomes:

Rbottom = (R2 * RL) / (R2 + RL), then Vout_loaded = Vin * (Rbottom / (R1 + Rbottom))

The load always pulls output voltage down compared to the unloaded calculation. For better stability, use divider resistor values significantly lower than the load resistance. A common design rule is to keep load current much smaller than divider branch current so the ratio does not shift too much.

Reference Ratios (Unloaded)

Target Vout/Vin	R1 : R2	Example Pair	Typical Use
1/2 (0.50)	1 : 1	10k : 10k	Simple midpoint reference
1/3 (0.333)	2 : 1	20k : 10k	Scaling 12V to ~4V
1/4 (0.25)	3 : 1	30k : 10k	Scaling for low-voltage inputs
1/10 (0.10)	9 : 1	90k : 10k	High-voltage measurement front end

About This Tool

This calculator helps you move from a basic divider estimate to practical circuit planning. You get both unloaded and loaded output voltage, effective resistance with a connected load, attenuation in linear and dB terms, and resistor power dissipation. That gives you the numbers needed to choose resistor values and wattage ratings with fewer surprises on real hardware.

For quick checks, set input voltage and ratio presets to see the expected node voltage instantly. For design validation, add a realistic load resistor. If loaded output is far below the unloaded result, the divider is too weak for your load and should be rebalanced with lower resistor values or buffered with an op-amp stage.

All calculations run locally in your browser. No circuit values leave your device.

Voltage Divider Calculator FAQ

What is a voltage divider?

A voltage divider uses two resistors in series to produce an output voltage that is a fraction of the input voltage.

What is the divider formula?

For an unloaded divider, Vout = Vin × (R2 / (R1 + R2)). R1 is the top resistor from Vin to Vout, and R2 is the bottom resistor from Vout to ground.

Why does output voltage drop when I connect a load?

The load resistor sits in parallel with R2, reducing effective bottom resistance. That lowers the divider ratio and reduces Vout.

How do I make divider output more stable under load?

Choose divider resistors much smaller than the load resistance so the load has less effect, while checking power and current limits.

Does this tool store my circuit values?

No. All calculations run in your browser and no values are sent to a server.

Related Tools

Brick Calculator -- Calculate how many bricks you need for a wall, patio, or project with mortar
Electrical Load Calculator -- Calculate total electrical load, amperage, and recommended breaker size for
FOV Visualizer -- Visualize and calculate field of view angles for cameras, games, and VR
Stair Calculator -- Calculate rise, run, number of steps, and code compliance for stairs