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⚡ Voltage Divider Calculator

Calculate output voltage from a resistor divider circuit. Essential for level shifting, sensor interfaces, and voltage reference circuits.

🔧 Calculate Voltage Divider

Vin R1 Vout R2 GND
The voltage you want to divide down
Top resistor
Bottom resistor

📐 The Voltage Divider Formula

Vout = Vin × (R2 / (R1 + R2))
Output voltage equals input voltage times the ratio of R2 to total resistance

A voltage divider is one of the most fundamental circuits in electronics. It uses two resistors in series to reduce an input voltage to a lower output voltage. The output is taken from the junction between the two resistors.

How It Works

  1. Current flows from Vin through both resistors to ground
  2. Each resistor drops a portion of the voltage (proportional to its resistance)
  3. Vout is measured across R2, giving you the divided voltage

Quick Reference Ratios

R1 : R2 Ratio Vout / Vin Example (12V in)
1:1 (equal) 50% 6V
2:1 33% 4V
1:2 67% 8V
3:1 25% 3V
1:3 75% 9V
9:1 10% 1.2V

🎯 Common Use Cases

🔌 Level Shifting

Connect a 5V sensor output to a 3.3V microcontroller input safely.

🔋 Battery Monitoring

Measure a 12V battery with an ADC that only accepts 0-3.3V.

📊 Potentiometer

A potentiometer is essentially a variable voltage divider.

🎚️ Volume Controls

Audio volume controls use voltage dividers to attenuate signals.

⚠️ Loading Effects Warning

Voltage dividers are only accurate when the load resistance (what you connect to Vout) is much higher than R2. If your load draws significant current, it will change the output voltage. For low-impedance loads, consider using a buffer amplifier or voltage regulator.

💡 Design Example

Problem: You want to measure a 12V car battery with an ESP32 ADC (max 3.3V).

Step 1: Choose the Ratio

We need: Vout = 3.3V when Vin = 14.4V (fully charged battery)

Ratio = 3.3 / 14.4 = 0.229 ≈ R2 / (R1 + R2)

Step 2: Select Resistor Values

If R2 = 10kΩ, then R1 = (14.4/3.3 - 1) × 10k = 33.6kΩ

Use standard values: R1 = 33kΩ, R2 = 10kΩ

Step 3: Verify

Vout = 14.4 × (10k / (33k + 10k)) = 14.4 × 0.233 = 3.35V ✓

💡 Pro Tip

Use higher resistance values (10kΩ+) to minimize current draw. Lower values waste power and drain batteries faster.

❓ Frequently Asked Questions

Can I use a voltage divider to power a circuit?

Generally no. Voltage dividers can't supply significant current. The output voltage drops as you draw more current. Use a voltage regulator (like LM7805 or LDO) for powering circuits.

What resistor values should I use?

For signal-level applications (sensors, ADCs), use 1kΩ to 100kΩ. Higher values save power but are more susceptible to noise. Lower values can handle more loading but waste power.

Does the voltage divider work with AC?

Yes, for resistive dividers with lower frequencies. At high frequencies, consider using capacitive dividers or accounting for parasitic capacitance.

How do I calculate R1 if I know Vout and R2?

R1 = R2 × ((Vin / Vout) - 1). For example, to get 3.3V from 12V with R2 = 10kΩ: R1 = 10k × (12/3.3 - 1) = 26.4kΩ