Voltage Divider Calculator

How do I use a voltage divider calculator?

Two resistors in series split a voltage in proportion to their size - the trick behind most sensor circuits. Enter the known values and inspect the result immediately. For example, Use 12 V, a 2 kΩ upper resistor, and a 1 kΩ lower resistor to calculate a 4 V output. Use the output to check your reasoning or shortlist a design, then verify the units, assumptions, and real-world limits that apply.

Try it

R1 and R2 in series - the tap between them is Vout

Input voltage

R1 (top resistor)

R2 (bottom resistor)

Output voltage6V

Current3mA

Understand the result

What's going on

Two resistors in series don’t just add their resistance - they also split whatever voltage is pushed across them, in proportion to their size. Tap the point between them and you get a smaller, predictable voltage. It’s how a 5 V sensor talks to a 3.3 V microcontroller pin without a special chip.

The formula

Vout = Vin × R2 / (R1 + R2)

Vout is measured across R2 - the resistor between the tap point and ground.

Show the derivation, mnemonic, and worked example

Build it up

The same current flows through both resistors - it’s one series path. Each resistor’s share of the total voltage matches its share of the total resistance: a resistor that’s half the total resistance carries half the total voltage. Tap the midpoint between R1 and R2 and you read out whatever share R2 holds.

Worked example

Vin = 9 V, R1 = 1,000 Ω, R2 = 2,000 Ω

Vout = 9 × 2000 / (1000 + 2000)

Vout = 9 × 0.667 = 6 V

Questions engineers ask

What should I enter in the Voltage Divider Calculator?

Use known values in the units shown beside each field. Keep every input within a realistic range and convert units before comparing the result with another source.

Can I use the Voltage Divider Calculator result directly?

It does not replace datasheet limits, tolerances, protection, thermal checks, measurement, or application-specific validation

How should I verify the Voltage Divider Calculator result?

Repeat the worked example, check the units and assumptions, then compare the output with a second calculation, a trusted reference, or a measurement from the real system.

How do I use a voltage divider calculator?

Understand the result