How the resistor search works
The ideal ratio is easy to calculate, but you can only buy standard values. This calculator pairs every value in the chosen E-series, from 1 Ω to 10 MΩ, with its best partner, discards pairs outside your total-resistance window, and returns the pair with the smallest output error.
- Voltage divider:
V_out = V_in·R2/(R1+R2) - Regulator feedback:
V_out = V_ref·(1 + R1/R2)
Worked example: 3.3 V from 5 V
From the E24 series with a total between 10 kΩ and 100 kΩ, the best pair is R1 = 4.7 kΩ and R2 = 9.1 kΩ, giving 3.297 V: an error of −0.09% while drawing about 0.36 mA.
Good to know
- High-value dividers save power but are pulled by ADC input current. Buffer the output or keep the divider current well above the load current.
- Pro shows the worst-case output with your resistor tolerance and the next four best pairs.