function equalise_columns() { var left_colh = document.getElementById("leftnav").offsetHeight; var main_colh = document.getElementById("content").offsetHeight; var common_h = Math.max(left_colh, main_colh); document.getElementById("leftnav").style.height = common_h + 'px'; document.getElementById("content").style.height = (common_h - 12) + 'px'; }