What is a voltage divider?

A simple passive circuit that scales down an input voltage using two series resistors.

How does a load resistor (RL) affect the output voltage?

A load resistor in parallel with R2 reduces the effective resistance of the bottom leg, causing the output voltage to sag.

Can I use a voltage divider to power high-current devices?

No, voltage dividers are inefficient for power delivery and suffer from severe voltage sag under heavy loads; use a voltage regulator instead.

What formula is used to calculate the output voltage?

The ideal output voltage is calculated using the formula Vout = Vin * R2 / (R1 + R2).

How do I find the value of R2 for a target output voltage?

Select the 'Find R2' mode, enter Vin, R1, and your target Vout, and the tool will calculate R2 using R2 = R1 / (Vin/Vout - 1).

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Voltage Divider Calculator

Calculate divider output voltage, solve for R1 or R2, and evaluate load effects with a circuit diagram

Details

What this tool helps you do

A voltage divider taps a fraction of the input voltage across two series resistors.

Equations:

Output voltage: Vout = Vin · R2 / (R1 + R2)
Solve R2: R2 = R1 / (Vin/Vout − 1)
Solve R1: R1 = R2 · (Vin/Vout − 1)

Load effect: a load RL in parallel with R2 sags Vout; the tool reports both ideal and loaded output.

Execution

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Prepared example runs

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2 examples

Halve 12 V with two equal resistors

R1 = R2 = 10 kΩ, Vin = 12 V → Vout = 6 V.

<div>Vout ≈ 6 V, divider current 0.6 mA.</div>

Design a 3.3 V output from a 5 V supply

Fix R1 = 10 kΩ and find R2 that yields Vout = 3.3 V.

<div>R2 ≈ 19.4 kΩ gives Vout = 3.3 V.</div>

Inputs

Set the required fields, then run the tool.

6 options

SettingsAdjust formats, ranges, numbers, and modes.6

Calculation ModeselectOptionalSupply Voltage (Vin)numberRequiredTop Resistor (R1)numberOptionalBottom Resistor (R2)numberOptionalDesired Output Voltage (Vout)numberOptionalLoad Resistor (RL, optional)numberOptional

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Samples

Voltage Divider Calculator

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Use cases

Examples

1. Halve 12 V with two equal resistors

2. Design a 3.3 V output from a 5 V supply

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