Voltage Divider Calculator
Two resistors in series split a voltage in proportion to their values — the basis of sensor scaling, level shifting (5 V to 3.3 V), and ADC reference inputs. This calculator works both ways: output voltage from two resistors, or the second resistor needed for a target output.
Formulas: Vout = Vin × R2 ÷ (R1 + R2) · R2 = R1 × Vout ÷ (Vin − Vout)
Worked example: 5 V across 1 kΩ and 2 kΩ: Vout = 5 × 2000 ÷ 3000 = 3.33 V — the classic 5 V to 3.3 V level shift. For a target of exactly 3.3 V from 5 V with R1 = 1 kΩ: R2 = 1000 × 3.3 ÷ (5 − 3.3) ≈ 1941 Ω, nearest standard value 2 kΩ. Note the warning: a divider's output voltage sags when the load draws current, so dividers suit signals and references, not powering loads — use a regulator for power.
For the resistor values themselves, use the resistor color code calculator.
Frequently asked questions
Can a voltage divider power a circuit?
Not reliably. Any load connected across R2 draws extra current and pulls the output voltage down. Dividers are for signals, sensor scaling and references; use a voltage regulator for power.
Why 5 V to 3.3 V with 1 kΩ and 2 kΩ?
Because 2000 ÷ (1000 + 2000) = 2/3, and 5 V × 2/3 = 3.33 V — close enough for most 3.3 V logic inputs, which accept a range around 3.3 V.
Does resistor tolerance matter?
Yes: with 5% resistors the output can shift by roughly 5% too. For precision references use 1% resistors and check the output with a meter.