Voltage Divider Calculator
A voltage divider is two resistors in series across a supply: the output is tapped between them and equals Vin × R2 / (R1 + R2). It is the simplest way to scale a voltage down — for a reference, a sensor bias, or an ADC input. This tool works two ways. Give it Vin, R1 and R2 and it returns Vout, the current through the chain (Vin / (R1 + R2)), the total power drawn, and the power dissipated in each resistor so you can check resistor ratings. Or switch to the reverse mode: enter Vin, R1 and the output voltage you want, and it solves for the R2 = R1 × Vout / (Vin − Vout) you need. Resistor values accept Ω, kΩ or MΩ units, and current and power are auto-scaled to µA/mA/A and µW/mW/W.
Output voltage
6 V
Formula: Vout = Vin × R2 / (R1 + R2)
Current
60 mA
Total power
720 mW
Power in R1
360 mW
Power in R2
360 mW
R1 is the top resistor to Vin; R2 is the bottom resistor to ground, across which Vout is measured. Output is unloaded — a load across R2 lowers Vout.
How to use
- Pick a mode: 'Compute Vout' (you know both resistors) or 'Find R2' (you know the target output).
- Enter the supply voltage Vin and resistor values with their units.
- Read Vout (or the suggested R2), the chain current, and the power in each resistor.
Frequently asked questions
- What is the voltage divider formula?
- Vout = Vin × R2 / (R1 + R2), where R1 is the top resistor (to Vin) and R2 is the bottom resistor (to ground, across which Vout is measured).
- How do I pick R2 for a specific output voltage?
- Switch to 'Find R2' mode and enter Vin, R1 and the target Vout. The tool solves R2 = R1 × Vout / (Vin − Vout). The target must be below Vin.
- Does this account for load current?
- No — it gives the unloaded (open-circuit) output. Connecting a load in parallel with R2 lowers Vout. Keep the divider current well above the load current, or use a buffer, for a stable output.
- Why does it show power per resistor?
- So you can choose resistors that won't overheat. The same current flows through both, so P = I²R for each; pick parts rated above the displayed value.
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