Resistor Divider Calculator

Enter any two of parameters R1, R2 or K. Then hit the button of the desired parameter.

Design Example:
Suppose you need an attenuation of K=0.1 and already have R2=1000.
What value of R1 is needed? Enter the two known parameters and hit "Get R1".

Schematic

R Divider

Enter Components

Download / Basics

To run or modify on your PC, download a simple version of this file with image (*.zip).
For a quick tour of some JavaScript / HTML basics, check out Inside the Code.

JavaScript

This code features 3 separate function calls, one per "Getx" button.

//////////////////////////////////////////////
// calc R1
//////////////////////////////////////////////
function getR1_Divider() {
   // get values directly from form  
   var R2=document.myForm.R2.value
   var K=document.myForm.K.value
   var R1
   
   // calc 
   R1 = R2*(1-K)/K;
   // place in text box
   document.myForm.R1.value = (R1).toPrecision(4);
}

//////////////////////////////////////////////
// calc R2
//////////////////////////////////////////////
function getR2_Divider() {
   // get values directly from form
   var R1=document.myForm.R1.value
   var K=document.myForm.K.value
   var R2
   
   // calc 
   R2 = R1*K/(1-K);
   // place in text box
   document.myForm.R2.value = (R2).toPrecision(4);
}

//////////////////////////////////////////////
// calc K
//////////////////////////////////////////////
function getK_Divider() {
   // get values directly from form
   var R1=document.myForm.R1.value
   var R2=document.myForm.R2.value
   R1=Number(R1);
   R2=Number(R2);
   var K
   
   // calc
   K=R2/(R1+R2);
   // place in text box
   document.myForm.K.value = (K).toPrecision(4);
}
///////////////////////////////////////////////

HTML

Each input button calls its own JavaScript function when clicked.

R1 Ohms			R1 = R2*(1-K)/K
R2 Ohms			R2 = R1*K/(1-K)
K (V/V)			K = R2/(R1+R2)