The ratio sets the unloaded output
R₁ connects the input supply to the output node. R₂ connects that node to the common return. With no load attached, the output is the input multiplied by R₂ divided by the sum of both resistors.
Two 10 kΩ resistors on a 5 V supply give 2.5 V and draw 250 µA. Scaling both resistances by the same factor preserves the nominal ratio but changes the current and the output resistance.
Opposite tolerance corners set the extremes
For positive resistances and a fixed nonnegative input voltage, raising R₁ lowers the output; raising R₂ increases it. The minimum output therefore pairs the largest R₁ with the smallest R₂. The maximum uses the opposite pair.
With independent ±1% tolerances, R₁ and R₂ may each lie between 9.9 kΩ and 10.1 kΩ. Substituting the opposite extremes gives the range below. Moving both resistors by the same percentage would leave the ratio unchanged and miss these cases.
| Case | R₁ | R₂ | Output |
|---|---|---|---|
| Minimum | 10.1 kΩ | 9.9 kΩ | 2.475 V |
| Nominal | 10 kΩ | 10 kΩ | 2.5 V |
| Maximum | 9.9 kΩ | 10.1 kΩ | 2.525 V |
A connected load changes the ratio
A resistive load from the output to return sits in parallel with R₂. For example, placing 100 kΩ across the lower 10 kΩ resistor makes the effective lower resistance about 9.091 kΩ. The nominal output becomes about 2.381 V, rather than 2.5 V.
The divider calculator reports the unloaded result; it does not include that load. An ADC input can be more complicated than a fixed resistance because it may charge an internal sampling capacitor. Check its acquisition requirements as well as its DC input specifications.
Keep a separate error budget
The reported minimum and maximum cover resistor tolerance only. Supply variation, temperature drift, bias current, leakage, and self-heating can move the output further. Verify resistor voltage and power ratings independently.
Worst-case bounds describe allowed combinations, not the probability of seeing them. A matched resistor network may specify ratio tracking separately from absolute resistance tolerance. Use the manufacturer’s ratio specification when that is what your design relies on; do not assume two discrete parts track.
References & further reading
Equations describe the stated model. Worked values are rounded for reading; the calculator’s download retains its calculated precision. Read about our checks and their limits.