Voltage Divider Rule
How two resistors split a voltage, the formula, why loading ruins the result, and the practical rule for choosing divider resistor values.
Questions people ask
Why does my divider output drop when I connect something?
The load is in parallel with the lower resistor, which lowers the combined resistance and therefore the output. Use lower divider values, or buffer the output with an op-amp follower.
Can I use a divider to power a 5 V device from 12 V?
No. The output voltage depends on the current drawn, so it will sag and wander. Use a regulator or a DC-DC converter.
What resistor values should I pick?
Low enough that loading is negligible, high enough that the standby current is acceptable. For a high-impedance input, 10 kΩ to 100 kΩ is the usual compromise.
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Last updated 22 August 2026