Nvm, found it!
var columnGraphs = event.chart.graphs.filter(function(graph) { return graph.type === 'column' && graph.ownColumns; }); var redrawNeeded = false; columnGraphs.forEach(function(graph) { var newWidth = Math.floor(graph.width / graph.ownColumns.length * 0.8); if (chart.categoryAxis.equalSpacing) { newWidth = undefined; } if (newWidth !== graph.fixedColumnWidth) { graph.fixedColumnWidth = newWidth; redrawNeeded = true; } }); if (redrawNeeded){ chart.validateNow(); }