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Voltage Divider Calculator

Estimate the output of an unloaded two-resistor DC divider. R1 is between the supply and output node; R2 is between the output node and the reference node. Read the output relative to that reference. The two power figures describe ideal dissipation and help you understand how the supply voltage is shared. Check the resistor positions carefully: swapping the values changes the output voltage.

Enter every field, including explicit zeros when permitted. Decimal and scientific notation are accepted; commas, fractions and blanks are rejected. Each input must be finite and no larger than 1 billion in absolute value. Observe the units and positive-value requirements below.

Unloaded output voltage (V)8
Series current (A)0.004
R1 power (W)0.016
R2 power (W)0.032

How to use this calculator

  1. Match your inputs to the stated circuit model and field labels.
  2. Convert your quantities to the units printed next to each field.
  3. Select Calculate, or press Enter, and read the labeled results.

Formula and method

Vout = VinR2/(R1 + R2); I = Vin/(R1 + R2); resistor power = I²R.

The calculation runs in your browser. After changing an input, select Calculate again. Invalid inputs or undefined mathematical conditions hide the previous result so it cannot be mistaken for an answer to the new values.

Worked example

With 12 V, R1 = 1,000 Ω and R2 = 2,000 Ω, current is 12/3,000 = 0.004 A. Output across R2 is 8 V; the two resistors dissipate 0.016 W and 0.032 W.

Limitations and safety

Ideal-component calculation only. Component tolerance, heating, parasitic effects and frequency limits are not modeled. This output does not establish component ratings, wiring compliance or a safe circuit design. Have consequential designs checked by a qualified professional; do not use this tool as instructions for working on energized equipment. An attached load changes the result by appearing in parallel with R2; this page assumes no output load.

The fields accept signed numerical input, but positive-only component values and nonnegative time or frequency requirements are enforced by the calculation. Read each error message before changing a value. Results use floating-point arithmetic and are shown to approximately 10 significant digits; component tolerances generally do not justify using all those digits in a physical design.

Frequently asked questions

Can I use this to power a device?

An unloaded divider model does not account for a device drawing current. A load changes the voltage, so this result alone is insufficient.

Why are my units important?

The calculator uses exactly the units printed in the input labels. For example, a micro-unit is one millionth of a base unit, and a milli-unit is one thousandth. Entering a base-unit value into a prefixed-unit field changes the meaning of the input.

Does the answer establish a safe component rating?

No. The formula evaluates an ideal model. Ratings, tolerances, transients, installation requirements and environmental limits need a separate design assessment.

Review notes and reference

Reviewed October 3, 2026. The default worked example and an additional boundary or scaling check were tested against expected values. Validation checks included blanks, nonnumeric text and inputs outside the supported range. OpenStax University Physics formula reference provides the circuit theory behind this model. The text and worked example on this page are original.

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