JSFiddle - React, Tailwind, and code Playground

HTML

distanza: occhi <-> TV<input type="text" onkeyup="calc()"></input>cm
<div></div>

JavaScript

var ratioCm2Feet=2.54;
/*function calc1(form) {
  a = form.a.value;
  b = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/2.97869411418791);
  c = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/4.46804291661112);
  d = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/6.70206437491669);
  e = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/13.9626341144098);
  f = Math.round(Math.pow(Math.pow(a, 2)/1.31640624208984, .5)/27.9252682288196);
  form.total1.value = b;
  form.total2.value = c;
  form.total3.value = d;
  form.total4.value = e;
  form.total5.value = f;
}*/
res={
 '480p':2.97869411418791,
    '720p':4.46804291661112,
    '1080p':6.70206437491669,
    '4k':13.9626341144098,
    '8k':27.9252682288196
}
function diagonale2widescreenwidth(a){
 return Math.pow(Math.pow(a,2)/1.31640624208984,.5)
}
feet2cm=30.48;
function calc(){
 var cm=document.getElementsByTagName('input')[0].value*1,
    div=document.getElementsByTagName('div')[0];
    div.innerHTML='<b>Distance:</b><br>'+
        'Feet '+(cm/(ratioCm2Feet*12)).toFixed(2)+'<br>'+
        'Inches '+(cm/ratioCm2Feet).toFixed(2)+'<br>'+
        'Meter '+(cm/100).toFixed(2)+'<br>'+
        '<b>Best TV (16:9) Diagonale:</b><br>'+
        (cm/ratioCm2Feet*.84).toFixed(0)+'" THX'+'<br>'+
        //diagonale2widescreenwidth(cm/ratioCm2Feet*.84)+' inches<br>'+
        //'Cm '+(cm*.84).toFixed(2)+'<br>';
        '720p PPI: '+(Math.sqrt(Math.pow(1280,2)+Math.pow(720,2))/(cm/ratioCm2Feet*.84)).toFixed(0)+
        ' @ Optimal: '+Math.round(diagonale2widescreenwidth(cm/ratioCm2Feet*.84)/res['720p'])*feet2cm+'cm<br>'+
        '4k PPI: '+(Math.sqrt(Math.pow(2*1920,2)+Math.pow(2*1080,2))/(cm/ratioCm2Feet*.84)).toFixed(0)+
        ' @ Optimal: '+Math.round(diagonale2widescreenwidth(cm/ratioCm2Feet*.84)/res['4k'])*feet2cm+'cm<br>'+
        '1080p PPI: '+(Math.sqrt(Math.pow(1920,2)+Math.pow(1080,2))/(cm/ratioCm2Feet*.84)).toFixed(0)+
        ' @ Optimal:...