Voltage Divider Calculator
Enter Vin, R1 and R2 to get the divider output, its current draw and the power dissipated in each resistor — plus the loading caveats that matter in practice.
Last updated: 2026-09-15
How the calculation works
- The output is the input scaled by R2/(R1+R2) — the fundamental resistive divider relation.
- Divider current and per-resistor power show whether standard 1/4 W parts survive.
- The notes flag loading: any current drawn from the output changes the ratio.
Formula
Vout = Vin × R2 / (R1 + R2) I = Vin / (R1 + R2)
| Symbol | Meaning | Unit |
|---|---|---|
Vout | Output voltage | V |
R1, R2 | Divider resistors | Ω |
I | Current through the divider | A |
Worked example
Interpreting the result
Dividers trade stiffness against current draw: lower resistances give a stiffer output but waste power. The rule of thumb is divider current ≈ 10× the load current. For ADC inputs, add a buffer or account for the input impedance — a 100 kΩ divider feeding a 10 kΩ ADC input shifts the reading by 9%.
Assumptions
- Unloaded output or load resistance ≫ R2.
- DC or low-frequency signals; stray capacitance affects fast edges.
Limitations
- Not a regulator — output sags with load and tracks Vin exactly.
- Resistor tolerance (1–5%) sets the accuracy floor; use precision parts for measurement dividers.
Frequently asked questions
Can I power a device from a voltage divider?
No — dividers are for signals, not supplies. Any load current shifts the output; use a regulator (buck, LDO) for power.
How do I pick divider resistor values?
Start from the load: divider current should be ~10× load current. Then set the ratio R2/(R1+R2) to the target voltage and choose the nearest E96 values.