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A voltage divider is one of the simplest and most common circuits in electronics: two resistors in series split an input voltage down to a smaller output voltage, in a ratio set by the resistor values. This calculator solves for whichever value — input voltage, output voltage, or either resistor — is missing.
How it works
Enter any 3 of the 4 values (input voltage, R1, R2, output voltage) and leave the one you want to solve for blank. The calculator applies Vout = Vin × R2/(R1 + R2).
- Enter input voltage, Vin (V) — leave blank to solve for this.
- Enter r1 (Ω) — leave blank to solve for this.
- Enter r2 (Ω) — leave blank to solve for this.
- Enter output voltage, Vout (V) — leave blank to solve for this.
- Click Calculate to see your results.
Examples
Scaling down a 12V supply
A 12V input through a 1kΩ (R1) and 2kΩ (R2) divider produces an 8V output — useful for scaling a sensor or logic voltage down to a level a microcontroller can safely read.
Who should use it
- Electronics coursework on basic circuit analysis.
- Scaling a sensor or supply voltage down to a target level.
Industry applications
- Electronics and circuit design
- Embedded systems and sensor interfacing
Advantages
- Solves for any of the four variables, not just forward output-voltage calculation.
- Extremely common, foundational circuit — worth understanding well.
Limitations
- Idealized, no-load formula — doesn't account for current drawn from the output point in a real circuit.
Common mistakes to avoid
- Mixing up which resistor is R1 vs. R2 — this flips the ratio and gives the wrong output voltage.
- Ignoring loading effects — if the output feeds into something that draws real current, the actual voltage will differ from this idealized no-load calculation.
Best practices
- For sensitive measurements, use resistor values much smaller than whatever load impedance you're driving, to keep the loading effect negligible.
- Double-check which resistor sits between input-and-output vs. output-and-ground before entering values.
Tips
- If the output feeds into a microcontroller's high-impedance analog input, loading effects are usually negligible — but if it feeds into something drawing real current, verify with the actual load in the circuit, not just this idealized formula.