Flutter Adjusting the Height and Width of a TextField (FAHWT)

AVAILABLE:    5

To customize the width of a TextField, you can wrap it with a Container widget, like this:

Container(              
  width: 100.0,
  child: TextField(),
)

As for the height of a TextField, here's another approach using the TextStyle widget. You might find this helpful, as it allows you to manipulate the fontSize and/or the height:

Container(              
  width: 100.0,
  child: TextField(                                 
    style: TextStyle(
      fontSize: 40.0,
      height: 2.0,
      color: Colors.black,                  
    ),
  ),
)

Note that the height property in TextStyle is a multiplier of the font size, as described in the property's documentation:

The height of this text span, as a multiple of the font size.

When [height] is null or omitted, the line height will be determined by the font's metrics directly, which may differ from the fontSize. When [height] is non-null, the line height of the span of text will be a multiple of [fontSize] and be exactly fontSize height logical pixels tall.*

Lastly, but certainly not the least, you may want to explore the decoration property of the TextField. This property provides a variety of customization options:

TextField(                                
  decoration: const InputDecoration(
    contentPadding: EdgeInsets.symmetric(vertical: 40.0),
  ),
)