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Calculator

Voltage Divider Calculator

Work out the output voltage of a two-resistor divider — with optional load.

V
kΩ
kΩ
kΩ

Optional: what the output feeds, e.g. 10000 for a high-impedance ADC

Result

Output voltage
3.333 V
Division ratio
0.6667
Current from source
167 µA
Power in divider
833 µW
  • !Too high for a 3.3 V pin (3.33 V) — raise R1 or lower R2.
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How it works

A voltage divider uses two resistors in series to turn a higher voltage into a lower one. It is the standard way to scale a battery voltage down so an ADC pin can measure it, or to level-shift a 5 V signal for a 3.3 V board such as the ESP32 or Raspberry Pi Pico.

The output only holds when whatever you connect to it draws very little current. Add a load resistance below to see how a real load drags the voltage down. For battery monitoring, use large resistors (100 kΩ range) to keep standing current tiny.

Formula

UnloadedVout = Vin × R2 / (R1 + R2)
With loadR2' = R2 ∥ RL = (R2 × RL) / (R2 + RL), Vout = Vin × R2' / (R1 + R2')
CurrentI = Vin / (R1 + R2')

Worked example. Vin = 5 V, R1 = 10 kΩ, R2 = 20 kΩ gives Vout = 5 × 20 / 30 = 3.33 V — a classic 5 V → 3.3 V level shift for slow signals.

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Frequently asked questions

Can I use a voltage divider to power a device?

No. A divider only produces a stable voltage when almost no current is drawn. For power, use a regulator (LDO or buck converter).

What resistor values should I pick?

Choose the ratio first, then scale the values. 10 kΩ + 10 kΩ and 100 kΩ + 100 kΩ both halve the voltage; the larger pair wastes ten times less current but is more sensitive to loading and noise.

How do I measure a LiPo battery with an ESP32 ADC?

A 4.2 V full cell needs to be under 3.3 V at the pin, so use a 1:2 divider (for example 100 kΩ over 100 kΩ gives 2.1 V at 4.2 V). Add a 100 nF capacitor at the pin and calibrate in software — ESP32 ADCs are not linear.

Is a divider good for level shifting I2C or fast signals?

No — use a proper bidirectional level shifter for I2C and fast signals. A resistor divider is only suitable for slow, one-direction signals like a button or TX line.

Boards this helps with

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