How is a voltage divider calculated?
Vout = Vin · R2 / (R1 + R2). The ratio only depends on the two resistors; the divider current I = Vin / (R1 + R2) sets their overall scale.
Vout = Vin · R2 / (R1 + R2)
Voltage divider calculator
Give the ratio, the input voltage and the divider current: the calculator picks standard resistors (or pairs) with the lowest ratio error and checks their power.
Divider specification
Ratio examples (fractions accepted)
Comparison by series
Best divider found in each series, within the allowed current deviation.
| Series | R1 (top) | R2 (bottom) | Ratio | Error | Current | Parts |
|---|
Highlighted row: overall best divider. Ratio = R2 / (R1 + R2).
Frequently asked questions
How do I choose the divider current?
Higher current makes the output stiffer against the load (an ADC input, for example) but dissipates more power. A divider current at least 10× the load current is a common rule of thumb.
What is the worst-case output voltage?
The worst case assumes R1 and R2 drift in opposite directions within their tolerance. With 1 % parts, a 0.5 ratio can move by about ±1 %; tighter tolerances reduce it proportionally.