Percentage is being automatically added to Google Pie charts tooltips, and there is no built-in option to remove it. However, you can use wpDataChart callbacks to tweak this. Charts usually support custom options appropriate to that visualization. You can use it for adding options that are available in Google Api. In this callback in method wpDataChartsCallbacks 83 is the ID of the chart we want to remove the percentage from the tooltips.

<script type="text/javascript"&gt
jQuery(window).on('load',function(){
    if( typeof wpDataChartsCallbacks == 'undefined' ){ wpDataChartsCallbacks = {}; }
    wpDataChartsCallbacks[96] = function(obj){
        obj.options.tooltip = {
                    text: 'value'
        }
        obj.options.pieSliceText = "none"
    }
});
</script>

Hover over the slices in the chart to see the change.