Voltage divider — Quick answer
A voltage divider uses two resistors in series to produce a fraction of the input voltage. Used for biasing, level shifting, and analog sensor scaling.
Vout = Vin × R2 / (R1 + R2)
- Vin — supply voltage (V)
- R1 — upper resistor (between Vin and Vout)
- R2 — lower resistor (between Vout and ground)
- Vout — tapped voltage (V)
Worked example: 12 V to feed a 3.3 V microcontroller ADC. Use R1 = 2 kΩ, R2 = 1 kΩ. Vout = 12 × 1k / (2k + 1k) = 12 × 0.333 = 4.0 V. (For exactly 3.3 V use R1 = 2.6k, R2 = 1k.) Current = 12/3k = 4 mA. Power = 48 mW.
Common voltage-divider outputs (Vin = 5 V)
| R1 | R2 | Vout | Use case |
|---|
| 10 kΩ | 10 kΩ | 2.50 V | Half-rail bias |
| 10 kΩ | 3.3 kΩ | 1.24 V | ADC reference scaling |
| 4.7 kΩ | 10 kΩ | 3.40 V | 5 V → 3.3 V level |
| 100 kΩ | 10 kΩ | 0.45 V | Voltage measurement (high impedance) |
| 1 kΩ | 100 Ω | 0.45 V | Low-impedance bias |
Standard / source: Ohm's law (IEC 60050); foundational electronics.
Used for: ADC input scaling for sensors, transistor base bias, op-amp reference voltage, audio attenuation, level shifting between logic families.
Standards & method
✓ Independently verified 12 July 2026- Basis
- First principles
- Method
- Ohm’s law and Kirchhoff’s voltage law. No standard governs these.
- Core formula
Vout = Vin × R2 / (R1 + R2)- Why this matters
- The formula assumes NO load on the output. Any load in parallel with R2 changes the ratio — if the load resistance is not ≫ R2, the divider will not deliver the calculated voltage.
- Independently verified
- 12 July 2026 — Formula re-derived from first principles and verified numerically against hand-computed reference cases, including edge cases and unit handling.
Results are for guidance. Verify against the current edition of the governing standard and have a licensed engineer review before construction or installation.
Voltage Divider Equation
A voltage divider is a simple linear circuit that produces an output voltage that is a fraction of its input voltage. Voltage division is the result of distributing the input voltage among the components of the divider.
Frequently Asked Questions
How do you calculate voltage divider?
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The output voltage is the input voltage multiplied by the ratio of the output resistor to the total resistance: Vout = Vin * (R2 / (R1 + R2)).
What is a voltage divider?
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A voltage divider is a simple circuit of two series resistors that produces an output voltage which is a fraction of the input voltage. The output is taken from the junction between the two resistors. Formula: Vout = Vin × R2 / (R1 + R2). It is one of the most fundamental circuits in electronics.
What are voltage dividers used for in electronics?
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Voltage dividers are used to: create reference voltages for ADC inputs on microcontrollers; level-shift signals (e.g., 5V to 3.3V logic); bias transistors and op-amps to their correct DC operating point; reduce sensor output voltages to ADC-compatible levels; and create DC operating points in audio amplifiers.
Why can a voltage divider not drive heavy loads?
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A voltage divider is only accurate when the load resistance is much larger than R2 (at least 10× greater). When a load is connected in parallel with R2, it reduces the effective resistance and pulls the output voltage lower than calculated. For driving loads, use a voltage regulator IC or op-amp buffer following the divider.
How do I select R1 and R2 values for a voltage divider?
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Choose values so that: (1) the ratio R2/(R1+R2) equals your desired voltage fraction; (2) the total resistance is low enough to supply sufficient current to the load, yet high enough to avoid excessive quiescent power loss. A practical guideline is to make the divider current 10 times the expected load current to maintain regulation.
What is the loading effect on a voltage divider?
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The loading effect reduces the output voltage when a load (RL) is connected in parallel with R2. Actual loaded output: Vout = Vin × (R2‖RL) / (R1 + R2‖RL), where R2‖RL = (R2 × RL)/(R2 + RL). The output drops significantly when RL approaches R2 in value. Keeping R1 and R2 small relative to RL minimises this effect.