check file size in flutter code example
Example 1: flutter check file size
file.lengthSync()
Example 2: how to get File height and width in flutter
File image = new File('image.png'); // Or any other way to get a File instance.
var decodedImage = await decodeImageFromList(image.readAsBytesSync());
print(decodedImage.width);
print(decodedImage.height);