JSFiddle - React, Tailwind, and code Playground

HTML

<input class="dlina">
<input class="wirina">
<input class="tolwina">
<input class="plotnostb">
<input class="ves" disabled>

JavaScript

$('input').on('change',function(){
  var D = parseInt($('.dlina').val(),10);
  if(!D) D = 0;
  var W = parseInt($('.wirina').val(),10);
  if(!W) W = 0;
  var T = parseInt($('.tolwina').val(),10);
  if(!T) T = 0;
  var P = parseInt($('.plotnostb').val(),10);
  if(!P) P = 0;
  var R = ((D/1000) * (W/1000) * (T/1000)) * P;
  $('.ves').val(R);
});