Electrical and electronics
Voltage divider calculator
Calculate the output of a two-resistor voltage divider with or without a load, or find the bottom resistor for a target voltage with the nearest E24 and E96 values.
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Result
Method and limits
Two resistors in series across Vin share it in proportion: Vout = Vin × R2 / (R1 + R2). A load RL across R2 is in parallel with it, so R2 is replaced by R2 ∥ RL = R2 RL / (R2 + RL) and the output falls. The divider behaves as a source of Vout behind R1 ∥ R2 (its Thevenin resistance). Solving for R2 gives R2 = R1 × Vout / (Vin − Vout).
Worked example: 12 V, R1 = 10 kΩ, R2 = 4.7 kΩ gives 12 × 4.7 / 14.7 = 3.837 V and 0.816 mA.
Limits
Ideal resistors at their nominal values are assumed; a 1% tolerance on each part moves the output by up to about 2%. A divider is not a regulator: the output changes with load and input, and it wastes the divider current continuously.
References
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