wat.js

var nodes = document.querySelectorAll(".js-setLabelWidth");
var elementWidths = [];


var widths = nodes.map(function(node) {
    var width = getComputedStyle(node)["width"];
    return parseInt(width, 10);
});

var maxWidth = (widths.reduce(Math.max, 0) + 1) / 16;

nodes.forEach(function(node) {
    node.style.width = maxWidth + "rem";
});