Voltage Divider Calculator

About Voltage Divider

Use this free Voltage Divider Calculator to quickly get accurate results in seconds, free and instantly offline with no signup required ever, trusted by professionals in Austin, Chicago, Miami, Denver, Seattle, and New York for reliable daily use without accounts, subscriptions, limits, or delays on any device for everyday personal and business workflows daily.

A voltage divider is a simple circuit that reduces a higher input voltage to a lower output voltage using two resistors in series. The output voltage is taken across the lower resistor (R2).

Formula: Vout = Vin × R2 / (R1 + R2)

Key points:

The ratio R2/(R1+R2) determines the voltage division
Current flows through both resistors: I = Vin / (R1 + R2)
Power dissipated: P = Vin² / (R1 + R2)
For sensor circuits, R2 is often the sensor (thermistor, photoresistor, etc.)

Loading effect: If the output connects to a load with finite impedance, the effective resistance of R2 changes. The load should be ≫ R2 to avoid significant voltage drop.

ADC references: Austin sensor startups biasing $200,000 thermistor fleets scale 5V sensors to 3.3V ADC windows precisely. New York labs calibrating $100,000 benches verify divider math before trusting readings on 09/22/2026.

Loop scaling: Chicago factories scaling $900,000 4-20mA loops drop sense voltages microcontrollers digest. Denver solar installers tapping $25,000 arrays monitor strings without frying inputs.

Marine rails: Miami shops dropping $3,000 12V rails to gauge levels pick sealed resistors that survive salt air. Seattle audio builders setting $5,000 preamp gains tune dividers by ear after math.

Loading discipline: Loads must dwarf R2 — buffer with op-amps when they cannot, or watch outputs sag under demand.

Power budgets: Divider current flows 24/7 — megohm values sip battery in field devices that must last years.

Where it is used

Setting reference voltages for ADCs, creating sensor voltage dividers, biasing transistors, reducing voltage for microcontroller inputs, potentiometer circuits Austin sensor startups bias $200,000 thermistor fleets, Chicago factories scale $900,000 4-20mA loops, Miami marine shops drop $3,000 12V rails, Denver solar installers tap $25,000 arrays, Seattle audio builders set $5,000 preamp gains, and New York labs calibrate $100,000 benches.

Examples

5V to 3.3V Logic Level Shifting

vin:5

r1:1000

r2:2000

Result: Vout: 3.333 V, Current: 0.00167 A, Power: 0.00833 W

12V to 5V for Microcontroller

vin:12

r1:7000

r2:5000

Result: Vout: 5.0 V, Current: 0.001 A, Power: 0.012 W

Sensor Interface (10k Thermistor)

vin:3.3

r1:10000

r2:10000

Result: Vout: 1.65 V, Current: 0.000165 A, Power: 0.00054 W

Frequently Asked Questions

Can I use a voltage divider to power a device?

No. Voltage dividers are for signal-level voltages only. The output impedance is R1||R2, so any load current will cause voltage drop. Use a voltage regulator (LDO, buck converter) for powering devices.

How do I choose resistor values?

Choose values so the divider current is 10-1000× the load current. Typical values: 1kΩ–100kΩ. Lower values = stiffer output but more power waste. Higher values = less power but more susceptible to noise and loading.

What if R2 is a variable resistor (potentiometer)?

Then you have an adjustable voltage divider. Vout varies from 0 (wiper at bottom) to Vin × R2/(R1+R2) (wiper at top). Common for volume controls, sensor calibration, reference voltage adjustment.

Can I use more than two resistors?

Yes. For N resistors in series, Vout across Rk = Vin × (Rk / ΣRi). The principle is the same — voltage divides proportionally to resistance.

Noise pickup?

High values invite noise — keep under 100k without shielding, add caps across R2 for filtering.

Stored anywhere?

No. Math runs locally in your browser. No values are uploaded or stored.

Calculator Inputs