Voltage-divider calculator
Calculate divider output voltage, current and resistor power. Check how a resistive load and resistor tolerances affect your circuit.
Connect R1 from the supply to the output and R2 from the output to ground. The optional load RL is parallel to R2.
| Quantity | Result |
|---|---|
| R1 dissipation | 0.625 mW |
| R2 dissipation | 0.625 mW |
| Power delivered to load | 0 mW |
| Output resistance R1 ∥ R2 (without load) | 5 kΩ |
Larger resistors reduce standing current but increase sensitivity to loading. Output resistance helps assess compatibility with the next circuit.
Method and assumptions
Rb = R2 ∥ RL; Vout = Vin × Rb / (R1 + Rb)
Iin = Vin / (R1 + Rb); P(R1) = (Vin − Vout) × Iin; P(R2) = Vout² / R2
Without a load, Rb = R2. Minimum output uses maximum R1 and minimum R2; maximum output uses the opposite corner. Supply voltage and load resistance are fixed. Displayed powers are nominal, not worst-case rating requirements.
Example: 10 V, R1 = R2 = 100 kΩ and RL = 1 MΩ gives approximately 4.762 V. Without the load, the result is 5 V.
The model excludes source impedance, temperature drift, leakage and ADC sampling-capacitor transients. A divider is not a voltage regulator.
Reference and comparison example: DigiKey — Voltage Dividers: Simple Math, Serious Pitfalls. Reference tool: DigiKey Voltage Divider Calculator.
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