This LM317 voltage calculator finds the regulated output voltage from resistors R1 and R2, or the resistor needed for a target voltage. Enter your values above.
Formula
Vout = 1.25 × (1 + R2 ÷ R1)
R1 sits between OUT and ADJ (often 240 Ω); R2 goes from ADJ to ground.
Example
R1 = 240 Ω, R2 = 720 Ω: Vout = 1.25 × (1 + 720÷240) = 5.0 V.
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Frequently Asked Questions
How do I calculate LM317 output voltage?
Use Vout = 1.25 times (1 + R2/R1). With R1 = 240 ohm and R2 = 720 ohm, the output is 5 volts.
What is R1 for an LM317?
R1 is the resistor between OUT and ADJ, commonly 240 ohms, which sets the reference current path.
What is the minimum LM317 output?
About 1.25 V, the internal reference voltage, when R2 is zero.