Voltage Divider Calculator (Vout)
Give Vin, R1 and R2 to get Vin x R2 / (R1 + R2). A 9 V supply across a 1 kohm and 2.2 kohm pair reads 6.19 V at the tap, before any load current.
Vout (V)
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Voltage divider: computing Vout from Vin, R1 and R2
A voltage divider is just two resistors in series, with the output read across R₂: Vout = Vin · R₂ / (R₁ + R₂). Example: Vin = 9 V with R₁ = 1 kΩ, R₂ = 2.2 kΩ gives Vout = 9 · 2.2 / 3.2 ≈ 6.19 V, and the current through the chain is I = Vin / (R₁ + R₂). Critical caveat: the moment the next stage draws current from Vout, the output shifts. To stay stable, the divider should source at least 10× the load current. When the load is high-impedance, drop an op-amp voltage follower (a unity-gain buffer) right after the divider.
Applications: ADC reads, logic-level shift, references
If you want to read a resistive sensor (LDR, NTC thermistor, potentiometer) into an MCU ADC (Arduino 0–5 V, ESP32 0–3.3 V), a divider is usually the first thing you reach for. The same circuit level-shifts a 5 V signal down to 3.3 V (say, Arduino TX → ESP32 RX with R₁ = 1 kΩ, R₂ = 2 kΩ), gives you a simple voltage reference, and works as a passive audio attenuator in line-level circuits.
FAQ
Why does Vout drop under load? The load resistance sits in parallel with R₂, which lowers the effective bottom resistance and throws off the divider ratio.
Can I power a circuit with a divider? Only if the load is in the microamp range. For anything that draws real power, reach for a linear regulator (LDO) or a buck converter, since a divider just burns power as heat and sags badly.
What resistor values should I pick? For MCU sensor reads, 1–100 kΩ is the usual range. Go too low and you waste current; go too high and the divider gets noise-sensitive and starts depending on the load.
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The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.