App Bar Buttons Don't Fit

Question

I am trying to make a custom App Bar. However, the icons are too big and don't fit within the circle. I have tried every size from 16px upto 256px; the size is always too big.

My code is this:

    <div data-win-control="WinJS.UI.AppBar" aria-label="Navigation Bar" 
        data-win-options="{layout:'custom',placement:'top'}">
        <header aria-label="Navigation bar" role="banner">
            <button onclick="javascript:window.location = 'page2.html'" id="cmdHome" data-win-control="WinJS.UI.AppBarCommand" data-win-options="{icon:'url(images/button1.png)', type:'button'}"></button>
        </header>
    </div>