How to vary the thickness of doughnut chart, using ChartJs.?

var options = {        
     cutoutPercentage: 70
};

If you are using chart.js for Angular via ng2-charts you would do something like this in your component.html file:

// component.html file

<canvas baseChart [options]='chartOptions'>
</canvas>

// Do note that other required directives are missing in this example, but that I chose to highlight the 'options' directive

And do something like this in your component.ts file:

//component.ts file

chartOptions = {
  cutoutPercentage: 80
};

A helpful source of information: available chart directives and config options for the [options] directive

since version 2 the field has been renamed to cutoutPercentage.

cutoutPercentage
Number 50 - for doughnut, 0 - for pie
The percentage of the chart that is cut out of the middle.

It can be used like this

var options = {        
    cutoutPercentage: 40
};

more details here http://www.chartjs.org/docs/#doughnut-pie-chart-chart-options

Update: Since version 3

var options = {        
    cutout: 40
};

According to the documentation at release notes of 3.x

Doughnut cutoutPercentage was renamed to cutout and accepts pixels as numer and percent as string ending with %.

use, percentageInnerCutout, like:

var options = {        
    percentageInnerCutout: 40
};
myNewChart = new Chart(ct).Doughnut(data, options);

Demo:: jsFiddle