Voltage Divider Calculator
Works out the output of a two-resistor divider, the current it wastes, and — if you enter a load — how far the load pulls the output down.
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The formula
Vout = Vin × R2 ÷ (R1 + R2)
The output is the input scaled by R2 as a fraction of the total. Any load draws current through R1 as well, which is why a divider is a poor voltage source.
What to watch out for
A divider is easy to calculate and easy to misuse:
- It is not a power supply. Any load in parallel with R2 lowers the output. Enter a load above and watch the figure fall.
- Rule of thumb: divider current ten times the load current. That keeps the error small. Lower resistances waste more power but hold their voltage better.
- Fine for references and sensing. An ADC input or a comparator draws almost nothing, so a divider is exactly right there.
- Power matters at low resistance. 12 V across two 100 Ω resistors dissipates 720 mW — beyond a standard quarter-watt part.
Frequently Asked Questions
What does a voltage divider with two equal resistors give?
Exactly half the input, unloaded. Two 10 kΩ resistors on 12 V give 6 V.
Why does my divider output drop under load?
Because the load is in parallel with R2, reducing the effective bottom resistance. Use lower divider resistances, or buffer the output with an op-amp follower.
Can I use a divider to power something?
Almost never. Any real current draw collapses the output. Dividers are for sensing and reference voltages, not for supplying power.