jQuery grid-system - handing different row widths
Things I pondered:


What's with the underscores everywhere?
Why not use regular jQuery convention and use this instead of element in your each iterator?
What's the use-case for this? A regular user will never see the console, so logging to it doesn't help anyone.
Even if someone is watching the console, what's the point of warning them when the row is just summarily removed? At least give the user a chance to fix the problem. It's worse if you're not looking at the console - then stuff is just gone with no explanation.
And the warning, "You have too many columns", isn't really truthful. The problem is that the columns - even if it's just 1 - are too wide. You code isn't checking how many there are.
But mostly: Why use percentages? Just compare widths directly. Saves you a whole lot of trouble (and code)


This seems clearer to me:

function validateRowWidth() {
  $('.row').each(function (index) {
    var row = $(this), // use `this`
        widthSum = 0;

    // sum up the (direct descendant) column widths
    row.children('[class*="size-"]').each(function () {
      widthSum += $(this).outerWidth(true); // 1 line is all you need here
    });

    // compare and warn if need be
    if(widthSum &gt; row.width()) {
      // alert is not a great choice, but it's better than console.log,
      // if this is user-facing. Explain the problem, and propose solutions.
      alert("Row " + index + " is too wide. Remove one or more columns or make them narrower.");
    }
  });
}