[Solved]-How to set highchart boxplot size-Highcharts

Use maxPointWidth or pointWidth option to control the box plot width.

Highcharts.chart('container', {
  series: [{
    type: 'boxplot',
    maxPointWidth: 50,
    data: [
      [760, 801, 848, 895, 965]
    ]
  }]
});

Demo:

https://jsfiddle.net/BlackLabel/w86xv14d/

API Reference:

https://api.highcharts.com/highcharts/series.boxplot.maxPointWidth https://api.highcharts.com/highcharts/series.boxplot.pointWidth