Engineering & Physics CalcyZone Calculator

Voltage Divider Calculator

Calculate the output voltage of a two-resistor divider.

Output voltage

3.8367 V

Divider current

0.8163 mA

Step-by-step working

Vout = Vin × R2 / (R1 + R2) = 12 × 4700 / (10000 + 4700) = 3.8367 V

Mathematical Formula

Vout = Vin × R2 / (R1 + R2) (unloaded).

Overview & Explanation

Two series resistors split a voltage in proportion to their values.

How It Works

Add R1 and R2.
Multiply Vin by R2 over the sum.

Practical Applications

ADC level shifting.
Sensor biasing.

How the divider formula works

Two resistors in series share the input voltage in proportion to their resistance. The output, taken across R2, is Vout = Vin x R2 / (R1 + R2). The same current flows through both resistors: I = Vin / (R1 + R2).

Example: 12 V with R1 = 10 kilohms and R2 = 4.7 kilohms gives 12 x 4.7 / 14.7 = 3.837 V, with 12 / 14,700 = 0.816 mA flowing. For a 5 V to 3.3 V logic shift, R1 = 1 kilohm and R2 = 2 kilohms give 5 x 2 / 3 = 3.333 V.

The loading effect

Anything connected to the output sits in parallel with R2 and lowers the effective resistance, which pulls the voltage down. Keep the load resistance at least about ten times R2. Dividers suit sensor and reference signals, not powering motors or LEDs; use a regulator for that.

Example 1: 12 V, 10 kΩ / 4.7 kΩ

≈ 3.84 V.

1

Inputs

Input voltage (V): 12 · R1 – top (Ω): 10000 · R2 – bottom (Ω): 4700

= entered

2

Step 1

Vout = Vin × R2 / (R1 + R2) = 12 × 4700 / (10000 + 4700) = 3.8367 V

3

Output voltage

Result

= 3.8367 V

Example 2: 5 V to 3.3 V

1.8 k / 3.3 k.

1

Inputs

Input voltage (V): 5 · R1 – top (Ω): 1800 · R2 – bottom (Ω): 3300

= entered

2

Step 1

Vout = Vin × R2 / (R1 + R2) = 5 × 3300 / (1800 + 3300) = 3.2353 V

3

Output voltage

Result

= 3.2353 V

How it's calculated & sources

Vout = Vin × R2 / (R1 + R2) (unloaded).

HyperPhysics (Georgia State Univ.) – Voltage divider

Frequently Asked Questions

Does a load change Vout?

Yes; a load in parallel with R2 lowers it. Keep load ≫ R2.

Can I power devices?

Dividers are for signals, not supplies.

Current?

Vin / (R1 + R2).

Why not use very large resistors to save power?

Large values save current but make the output more sensitive to loading and noise. Values from 1 to 100 kilohms are common.

Do resistor tolerances matter?

Yes. 5% parts can move the output noticeably, so use 1% resistors where accuracy matters.

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