Electronics CalculatorsVoltage divider limits and loading
A divider is simple, but it assumes that nothing takes current from the output.
What happens with a load
The output of a divider is across R2. A load resistor connected to the output is in parallel with R2, which makes the lower part smaller and the output lower. The calculated values below are for a 5 V input.
| Load on the output (R1 = R2 = 10 kΩ, 5 V in) | Output voltage |
|---|---|
| No load | 2.5 V |
| 1 MΩ | 2.488 V |
| 100 kΩ | 2.381 V |
| 10 kΩ | 1.667 V |
| 1 kΩ | 0.4167 V |
Rules of thumb
- Make the load at least ten times larger than R2 (a hundred times if you need accuracy).
- A lower resistance keeps the output steadier under load, but wastes more current (V² / (R1 + R2) is always flowing).
- Use a buffer or a regulator when the load is not tiny.
What a divider is good for
Dividers are good for scaling a voltage to read it, for example in front of an analog input, and for setting a reference where nothing is drawn. They are not for power: use a regulator.
How do I get exactly 3.3 V from 5 V?
Use a regulator. A divider gives the value that the standard resistors allow and changes with load.
Do the resistor tolerances matter?
Yes: the output moves by about the sum of the tolerances. Use 1% parts for accuracy.
This is an independent guide. It is not connected with any standards body or company named here. The formulas are the usual textbook ones; the colour code, E-series and AWG values are those printed in common references, because the standards IEC 60062, IEC 60063 and ASTM B258 are paid documents that we did not read. Tables and examples were calculated with Python on 14 November 2026. Check data sheets and local safety rules before you build.