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Voltage Divider Calculator

Calculate the unloaded output voltage of a two-resistor divider from source voltage and resistor values, including divider current and resistor power dissipation.

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Voltage divider calculator: unloaded two-resistor output, current, and resistor power

A voltage divider calculator estimates the unloaded output of a simple two-resistor network from the source voltage and the two resistor values. This version also reports divider current, total resistance, and the power dissipated in each resistor so the output is easier to judge in a practical design context.

What this voltage divider calculator solves

This page models the classic two-resistor divider where one resistor sits above the tap point and the other sits below it. Once the source voltage and both resistor values are known, the calculator returns the unloaded output voltage at the midpoint.

In practice, output voltage alone is rarely enough. Divider current and resistor dissipation matter because they tell you whether the chosen values are wasting too much power or running too little current for the downstream use case.

The divider formula used here

For an unloaded two-resistor divider, the output is the source voltage multiplied by the lower resistor’s share of the total series resistance. That works because the same current flows through both resistors and the output node sits across the bottom resistor only.

The calculator also uses the total series resistance to derive divider current, then applies I²R to estimate how much power each resistor dissipates at the entered supply voltage.

Vout = Vin x R2 / (R1 + R2)

Calculates the unloaded midpoint voltage when R1 is the top resistor and R2 is the bottom resistor.

I = Vin / (R1 + R2)

Finds the current flowing through the divider string.

P = I² x R

Applies resistor dissipation separately to the top and bottom resistor.

How to interpret the result

A divider ratio near 50% means the two resistors are similar in value, while a very low or very high ratio means one resistor dominates the total. The power figures help show whether the divider is appropriate for a low-power reference network or whether it is burning more energy than needed.

The current value also tells you whether the divider is likely to hold its target voltage well when a small load is attached. A very weak divider can sag noticeably once the output node is loaded, because this page assumes the midpoint is unloaded.

What this simplified model leaves out

This version assumes no load is connected to the output node, so it does not account for loading effects, input impedance of downstream circuits, tolerance stack-up, noise, or temperature drift.

Use it as a first-pass design and education tool. If the divider feeds a real load or precision reference point, move to a loaded-divider analysis and check resistor tolerance and power ratings before finalizing the design.

Frequently asked questions

Why does the output change if I swap R1 and R2?

Because the output node is taken across the bottom resistor only. Swapping the resistor positions changes which resistor gets the output voltage share, so the ratio and the final output both change.

 What does unloaded mean in a voltage divider?

It means nothing is attached to the midpoint that draws current. In a real circuit, any connected load changes the effective lower resistance and can pull the output voltage away from the unloaded value.

 How do I know if the divider current is too low?

If the downstream input draws a meaningful fraction of the divider current, the unloaded estimate may not hold. As a rule of thumb, designers often want the divider current to be comfortably higher than the load current so the output stays stable.

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