Voltage Divider Calculator

Enter values to solve instantly. Includes unit conversions, divider visualization, and Show Work.

How to Use

  1. Enter Vin and either both resistors (R1, R2) or a target Vout.
  2. Select units (mV/kV, kΩ/MΩ) as needed.
  3. Enable “Load” to estimate loaded Vout using an optional load resistor.
  4. Open “Show Work” to see formulas and steps (base units).
Divider Schematic View
Visual feedback: ratio, Vout marker, and current estimate.
Vin
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Vout
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Idiv
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Ratio
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Hint: —
Vin Source V R1 R R2 R Vout Rload Drag handles: Vin, R1, R2 (quick what-if). Use inputs for exact values + units. Divider math assumes ideal resistors. Optional load estimates show real-world drop.
Inputs & Settings
Solve Vout from Vin, R1, R2 — or design R2 for a target Vout.
Common: 3.3V, 5V, 12V, 14.4V
Used in “Design R2” mode (solve for R2).
R1 is from Vin to Vout node.
R2 is from Vout node to ground.
Optional: output load to estimate loaded Vout.
Enter values to see divider current and suggestions.
Show Work (step-by-step)
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Work is shown in base units (V, Ω, A) for clarity and consistency.

Voltage Divider Formulas

Quick answer: For two resistors, the ideal output is Vout = Vin × (R2 / (R1 + R2)).

Optional load: replace R2 with R2 || Rload to estimate loaded output.

  • Ideal Vout: Vout = Vin × (R2 / (R1 + R2))
  • Divider current: I = Vin / (R1 + R2)
  • Design R2 (target Vout): R2 = (Vout × R1) / (Vin − Vout)
  • Loaded R2: Req = (R2 × Rload) / (R2 + Rload)
Where Vin/Vout in volts and resistances in ohms.

FAQ

Why does my divider voltage drop under load?

The load forms a parallel resistance with R2, lowering the effective bottom resistance and pulling Vout down.

What divider resistor values should I use?

Higher values reduce current draw but increase sensitivity to noise and load effects. Many signal dividers use 10k–100k ranges.

Can I power a device with a divider?

Usually no. A divider is best for sensing/reference, not powering loads (unless load current is tiny compared to divider current).

Tool Info

Last updated:

Updates may include UI improvements, unit support, and calculation edge-case handling.