Tableau - Create Donut Chart: Using 2 Pie Charts

Step 1: Create the Pie Chart 

1. Under Markers , select the Pie Chart marker type.
2. Drag Category to Color .
3. Drag the total number of tasks to Angle .
4. Drag the total number of tasks again and drop it on the label .
5. Resize the pie chart as desired. 

Step 2: Switch to a Dual Axis Chart

1. Right click on any field, create --> calculate field
2. In the Calculated Field dialog box that opens, do the following, and then click OK:
   1. Name this calculated field. In this example, the calculated field name is "Virtual Axis".
   2. In the formula field, enter the formula: MIN(1)
3. Drag the virtual axis to the row , drag the virtual axis to the row again .
4. On the row, right-click the second instance of the virtual axis and check Dual Axis .

Step 3: Change the second pie chart to a circle

1. At the bottom of the marks card, click Aggregate (virtual axis) (2) .
2. Remove categories from colors .
3. Remove task totals from angles and tags .
4. Click Color , and choose the same color as the background. In this example, click White.
5. Click Size , and drag the slider to the left to make the circle smaller.
6. Right-click on each axis and uncheck Show Titles .