Voltage divider calculator

Find standard resistor values that divide one voltage down to another, then check the tolerance, current and output resistance.

Values

Input voltage, V_in

Output you want, V_out

Resistor values

E12 and E24 are what most parts drawers hold. E96 is common for 1% resistors.

Resistor tolerance

Total resistance, at least

Total resistance, at most

Lower totals draw more current but drive an ADC better. When the same ratio fits several sizes, the one nearest the middle of your range is shown.

Results

Selected	R₁	R₂	V_out	Error	Current

Check a pair

Output
Current
Output resistance: R₁ and R₂ in parallel: what a load or ADC sees driving it.

Output with resistor tolerance

How it's calculated

V_out = V_in × R₂ / (R₁ + R₂)

For each standard value of R₂, the search finds the standard values of R₁ on either side of the ideal one and keeps the pairs whose total fits your range, best first.

The tolerance range is the worst case: the output is highest when R₁ is at the low end of its tolerance and R₂ at the high end, and lowest the other way round.

V_max = V_in × R₂(1 + t) / (R₁(1 − t) + R₂(1 + t))

All of this assumes nothing draws current from the output. A load in parallel with R₂ pulls the output down; keep the output resistance well below the load's input resistance, or buffer it.