Voltage divider calculator
Enter the input voltage and the two resistors: R1 on top and R2 at the bottom, where the output is taken.
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How to use it
- Enter input voltage, top resistor r1 and bottom resistor r2.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Vout = Vin × R2 ÷ (R1 + R2), current I = Vin ÷ (R1 + R2), power P = Vin × I.
Example
Inputs: Input voltage = 12 V, Top resistor R1 = 10,000 Ω, Bottom resistor R2 = 10,000 Ω. Result: Output voltage: 6 V; Divider current: 0.6 mA; Power dissipated: 0.0072 W.
Limits and caveats
- Assumes the output load draws negligible current; any load acts in parallel with R2 and lowers the output.
- A divider is not a power supply; use a voltage regulator to feed a load.
Questions about this tool
How do I drop 5 V to 3.3 V for a microcontroller input?
A 1.8 kΩ top and 3.3 kΩ bottom give about 3.24 V, which suits a signal input.
Should I use small or large resistors?
Large values waste less current but are more affected by the load. Values from 1 to 100 kΩ are common for signal lines.
Does tolerance affect the result?
Yes, 5% resistors can shift the output by a few percent. Use 1% parts when accuracy matters.