🔌 LM317 Resistor Calculator
Enter your R1 and R2 resistor values to calculate the output voltage of an LM317 adjustable regulator circuit.
What this calculator does
The LM317 is a popular adjustable linear voltage regulator whose output voltage is set by two external resistors. This calculator applies the standard datasheet formula to estimate the output voltage from your chosen R1 and R2 values.
How the calculation works
The formula is Vout = Vref × (1 + R2/R1) + (Iadj × R2), where Vref is the LM317’s internal reference voltage (typically 1.25V) and Iadj is its small adjustment pin current (typically about 50 microamps). The Iadj term is usually tiny compared to the rest, so both the full formula and the simplified version without it are shown.
Real-world resistor tolerances and the exact Vref of your specific chip will shift the actual measured voltage slightly from this calculated value.