Flutter increase height of TextFormField

Just adjust the contentPadding in InputDecoration.

final email = TextFormField(
    keyboardType: TextInputType.emailAddress,
    autofocus: false,
    initialValue: 'sathyabaman@gmail.com',
    style: new TextStyle(fontWeight: FontWeight.normal, color: Colors.white),
    decoration: InputDecoration(
      hintText: 'Email',
      contentPadding: const EdgeInsets.symmetric(vertical: 25.0, horizontal: 10.0),
      border: OutlineInputBorder(borderRadius: BorderRadius.circular(32.0)),
    ),
  );