Size a voltage divider for a sensor or level shift

The job

A 5 V sensor signal going into a 3.3 V microcontroller pin needs a divider: two resistors in series, signal tapped between them. Vout = Vin × R2 ÷ (R1 + R2) — but choosing actual resistor values is the fiddly part.

Solve any direction

Enter any three of input voltage, output voltage, R1, R2 — the fourth is computed. Then check the nearest E24 standard values for the computed resistance, since you can't buy 14.7 kΩ off the shelf.

• Larger resistors mean less wasted current but a weaker signal into high-impedance inputs — the tool shows the divider's current draw.
• The result assumes nothing else is connected to the output: any load in parallel with R2 drops the voltage further.

Worked example

5 V → 3.3 V: with R1 = 1 kΩ, R2 comes out ≈ 1.94 kΩ — nearest E24 is 2 kΩ, giving 3.33 V actual. Good enough for a logic-level shift; verify tolerance if you're feeding an ADC reference.

Where it stops

Unloaded two-resistor dividers only — no current regulation, no negative rails, no three-tap chains. For anything drawing real current, use a regulator; a divider's output sags as soon as the load is a fraction of R2.