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 tocutout
and accepts pixels as numer and percent as string ending with%
.