Lazarus/Delphi: Width and ClientWidth - Difference

Not long ago, we had a question in which someone has asked what the difference between Height and ClientHeight is in regard to Forms of Delphi and Lazarus. For the sake of completeness, now I would also like to explain the difference between Width and ClientWidth.

What are Width and ClientWidth?

Width and ClientWidth are properties defining the width of a form which is the width of the window. The property can be used in Lazarus as well as in Delphi.

• ClientWidth is referring to the width of the form or the window inclusive of the width of the lateral edges
• Width on the other hand is referring to the inner width of the window without taking the width of the lateral borders into account

The width of the border is determined by several factors: For example, it depends on the operating system, the current theme and even within the same operating system, there may be differences between each version. For instance, not all Windows versions are having the same border size for their applications.

When should I use which property?

Depending on your purpose of application, it is recommended to set the window size via Width or ClientWidth.

If we want to adjust the window exactly to the content therein using the exact pixel size, it is better to set the width via ClientWidth. Finally, in this case we do not know the resulting size of the window when an arbitrary border is added.

In case that the window itself should have a specific size, for example to ensure that it takes a specific size on the screen, we should set the width by using the Width property. In this case, ClientWidth will automatically have a little bit smaller value.