Detect browser height

browserheight

function browserHeight(){
  var headerHeight = $(window).height();
  $(".header").css('height',headerHeight); // I wanted to subtract pixels from this value, e.g. change 970px to 920px
};
$(document).ready(browserHeight);

function browserHeight(){
var headerHeight = parseInt($(window).height()) - 50;
$(".header").css('height',headerHeight+'px'); // I wanted to subtract pixels from this value, e.g. change 970px to 920px
};
$(document).ready(browserHeight);

You can use parseInt to abstract the number.

var num = parseInt(headerHeight, 10); // => 970
var newNum = num - 70;
$(".header").css("height", newNum + "px"); // might not be required, jQuery defaults to px IIRC