>> Open the table of layer
Right-click on the layer and open attribute table
>>Create a field for the property we will calculate.
Click on Option > Add Field…
>>Fill a form
Please carefully select what type of your field should be. In this example, I want to create a field contains 7 precision and 2 digits of decimal. If you have any question about what type of field suits you, you can ask me in comment below.
This step will give you an empty field like shown in the following image
Calculate the property
Righ click on our new field above > Calculate Geometry
In this example, I want to calculate are using UTM projection with hectares unit. Adjust this if you want to do different one.