I have written a page in HTML5 with a special form to accept numeric input only; however, it won't accept decimals

I've written a form (located at http://ift.tt/1IisadK) that uses numeric input, and the PHP script at http://ift.tt/1Iis9Xn will only accept numeric inputs. When I change the number in the URL bar to a decimal, it still works, so I know it's a problem with the form. How do I make it accept decimals?