Sample Size Calculator for a Proportion?

@import url(‘https://fonts.googleapis.com/css?family=Droid+Serif|Raleway’);

.axis–y .domain {
display: none;
}

h1 {
color: black;
text-align: center;
margin-top: 15px;
margin-bottom: 0px;
font-family: ‘Raleway’, sans-serif;
}

h2 {
color: black;
font-size: 20px;
text-align: center;
margin-bottom: 15px;
margin-top: 15px;
font-family: ‘Raleway’, sans-serif;
}

p {
color: black;
text-align: center;
margin-bottom: 15px;
margin-top: 15px;
font-family: ‘Raleway’, sans-serif;
}

#words_intro {
color: black;
font-family: Raleway;
max-width: 550px;
margin: 25px auto;
line-height: 1.75;
}

#words_intro_center {
text-align: center;
color: black;
font-family: Raleway;
max-width: 550px;
margin: 25px auto;
line-height: 1.75;
}

#words_outro {
color: black;
font-family: Raleway;
max-width: 550px;
margin: 25px auto;
line-height: 1.75;
}

#words {
color: black;
font-family: Raleway;
max-width: 550px;
margin: 25px auto;
line-height: 1.75;
padding-left: 100px;
}

#calcTitle {
text-align: center;
font-size: 20px;
margin-bottom: 0px;
font-family: ‘Raleway’, serif;
}

#hr_top {
width: 30%;
margin-bottom: 0px;
margin-top: 10px;
border: none;
height: 2px;
color: black;
background-color: black;
}

#hr_bottom {
width: 30%;
margin-top: 15px;
border: none;
height: 2px;
color: black;
background-color: black;
}

.input_label_calc {
display: inline-block;
vertical-align: baseline;
width: 350px;
}

#button_calc {
border: 1px solid;
border-radius: 10px;
margin-top: 20px;
padding: 10px 10px;
cursor: pointer;
outline: none;
background-color: white;
color: black;
font-family: ‘Work Sans’, sans-serif;
border: 1px solid grey;
/* Green */
}

#button_calc:hover {
background-color: #f6f6f6;
border: 1px solid black;
}

.label_radio {
text-align: center;
}

function calc() {
//get input values
var z = document.getElementById(‘z’).value*1;
var p = document.getElementById(‘p’).value*1;
var E = document.getElementById(‘E’).value*1;

//find number of bins
var n = Math.ceil(p*(1-p)*Math.pow((Math.abs(jStat.normal.inv((1-z)/2, 0, 1))/E), 2));

//output
document.getElementById(‘n’).innerHTML = n;
}