You can add a label or title for each axis in any Cartesian chart using the axis.scaleLabel property (for example, options.scales.xAxes[0].scaleLabel configures the title for the first x axis). The following table lists the configurable properties of a scaleLabel object:

The following code fragment adds titles for the x and y axes of a bar chart that we created in Chapter 3, Chart.js – Quick Start. Note that it's not enough to just add axis.scaleLabel.labelString, you also have to set axis.scaleLabel.display: true, since the titles are hidden by default:

scales: {
     xAxes: [{
         scaleLabel: {
             display: true,
             labelString: "Oceans",
             fontSize: 16
         }
     }],
     yAxes: [{
         scaleLabel: {
             display: true,
             labelString: "Volume in cubic km",
             fontSize: 16
         }
     }]
 }

See the full code in Cartesian/Cartesian-3-scaleLabel.html. The result is shown as follows: