Helium Calculator

HTML

<h2>Helium Calculator</h2>

<div class="left">Balloon Design: </div>
<select id="balloon_model">
  <option value="0.25">Latex 9" Round</option>
  <option value="0.5">Latex 11" Round</option>
  <option value="0.3">Latex 11" Heart</option>
  <option value="1.5">Latex 16" Round</option>
  <option value="2.0">Latex 18" Round</option>
  <option value="0.5">Foil/Mylar 18" (approx.)</option>
  <option value="1.15">Ultrashapes (approx.)</option>
  <option value="1.2">Bubbles (approx.)</option>
  <option value="2.0">Super Shapes (approx.)</option>
  <option value="2.0">Sing-A-Tune</option>
  <option value="8.0">Latex 3' (Inflated to 2.5)</option>
  <option value="15.0">Latex 3'</option>
  <option value="34.0">Chloroprene 4'</option>
  <option value="66.0">Chloroprene 5.5'</option>
  <option value="267.0">Chloroprene 8''</option>
</select>
<br />
<div class="left">QTY:</div>
<input id="qty" />
<hr />
<div class="left" style="text-align: right;">
  <input type="submit" id="btn" value="Calculate" />
</div>
<input type="text" id="result" readonly />Total ft3 p/balloon
<hr />

<input type="text" id="tankyouneed" readonly />Tank you need (disregard this result, just testing arrays)

CSS

.left {
  float: left;
  width: 200px;
}

JavaScript

var $ = document.getElementById.bind(document);

$('btn').addEventListener('click', function() {

  var

    tanks = {
      0: {
        name: 'HEL550',
        volume: 292
      },
      1: {
        name: 'HEL450',
        volume: 225
      },
      2: {
        name: 'HEL250',
        volume: 125
      },
      3: {
        name: 'HEL160',
        volume: 125
      },
      4: {
        name: 'HEL110',
        volume: 55
      },
      5: {
        name: 'HEL50',
        volume: 27.5
      },
      6: {
        name: 'BT 326502',
        volume: 14.9
      },

      7: {
        name: 'BT 306472',
        volume: 8.9
      }
    },

    balloonModel = $('balloon_model').value,
    qantity = $('qty').value,
    finalResult = balloonModel * qantity,
    finalResultRounded = finalResult.toFixed(2),
    tankCalc = tanks[7].volume;

  $('result').value = finalResultRounded;
  $('tankyouneed').value = tankCalc;


}, false);