Calculate voltage divider

Estimate unloaded output voltage and current for two series resistors across a supply.

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ToolVoltage Divider Calculator
Input
Output
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Preview

How it works

Output is Vin × R₂ ÷ (R₁ + R₂), and divider current is Vin ÷ (R₁ + R₂). The result assumes the output is unloaded.

  • R₂ is the lower resistor returning to ground.
  • Load resistance and tolerance are not inferred.

Worked example

5V down to 3.3V logic
R1 fixed at 1k, working out the R2 that gives a 3.3V output
Input
											Input voltage: 5
R1 ohms: 1000
Target output voltage: 3.3
Output
												Output voltage: 3.3
R1 ohms: 1000
R2 ohms: 1941.1765
Current amps: 0.0017
Power watts: 0.0085

When to use this

Sensor circuits scale voltage for ADCs, electronics lessons select reference resistors, and prototypes estimate divider current.

Edge cases

  • A load appears in parallel with R₂ and lowers output.
  • A zero resistor sum makes current undefined.
  • Tolerance can move real output beyond the ideal result.