Last Updated on November 9, 2026

Whenever you build a variable power supply, or you need a voltage that a 7805 or 7812 cannot give, the LM317 is the regulator most of us reach for. It is cheap, available in every electronics shop, and it can give anything from 1.25 V up to 37 V using just two resistors. But every time you need a new output voltage, you have to sit with the formula, work out the resistor pair, and then check whether that resistor value is actually available in the market.

So here is a simple LM317 Output Voltage Calculator from theoryCIRCUIT. Enter R1 and R2 and it gives you the output voltage. Here as per the datasheet suggestion R1 Value will be in 240Ω as default and you can change it if you want, then put R2 value. Input Voltage (Vin) and Load current value placed as optional for dropout and heat check, if you have those value then enter and get the output with suggestions from this calculator.

LM317

The LM317 IC is an Adjustable three terminal positive voltage Regulator. It gives Regulated output voltage Range from 1.25V to 37V with Output current up to 1.5A, LM317 IC can be used as fixed output voltage regulator by using fixed R1 (240Ω default) and fixed R2 values. Or adjustable voltage regulator by using variable R2 Resistor by using variable R2 Resistor by the way LM317 needs only two external Resistors to set output voltage. LM317 IC includes current limit, internal overload protection and thermal overload protection.

How this Calculator Works?

LM317 output Voltage formula

is the base for this calculator and it calculates using any two value to find out missing one.

Here is the simplified formula to find out Resistor R1 and R2 value,

As you know the LM317 is still one of the simplest ways to get any regulated DC voltage output from unregulated DC supply with just two Resistors. By using this LM317 output voltage calculator, you do not need to workout the formula every time.