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.
Open calculatorLast 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.
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.
Output of a 12 V divider for common resistor pairs
| R1 (top) | R2 (bottom) | Output (V) |
|---|---|---|
| 10 kΩ | 10 kΩ | 6.00 |
| 22 kΩ | 10 kΩ | 3.75 |
| 10 kΩ | 4.7 kΩ | 3.84 |
| 10 kΩ | 22 kΩ | 8.25 |
| 47 kΩ | 10 kΩ | 2.11 |
Vout = Vin × R2 ÷ (R1 + R2), with no load connected.
Scaling 5 V down towards 3.3 V
| R1 (top) | R2 (bottom) | Output (V) |
|---|---|---|
| 1 kΩ | 2 kΩ | 3.33 |
| 1.8 kΩ | 3.3 kΩ | 3.24 |
| 10 kΩ | 20 kΩ | 3.33 |
Worked scenario: what a load does to the output
Two 10 kΩ resistors across 12 V give 6.0 V with nothing connected. Add a 10 kΩ load in parallel with the bottom resistor and that half becomes 5 kΩ, so the output falls to 4.0 V. A divider only holds its voltage when the load draws much less current than the divider itself.
When a divider is the wrong tool
- Powering something: a divider wastes energy and its output sags as the load changes. Use a regulator.
- Reading a sensor with a high source resistance: buffer it, or use much higher resistor values with a high-impedance input.
- Precision work: resistor tolerance and temperature drift move the output, so choose tolerances to match the accuracy you need.
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.