In order to calculate a file’s size in C#, you can use the FileInfo object and create some logic to calculate the physical KB, MB or GB of a file. You can use the following code:

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.IO;namespace GetFilesize{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        public static string GetFileSizeInBytes(long TotalBytes)        {            if (TotalBytes = 1073741824) //Giga Bytes            {                Decimal FileSize = Decimal.Divide(TotalBytes, 1073741824);                return String.Format("{0:##.##} GB", FileSize);            }            else if (TotalBytes = 1048576) //Mega Bytes            {                Decimal FileSize = Decimal.Divide(TotalBytes, 1048576);                return String.Format("{0:##.##} MB", FileSize);            }            else if (TotalBytes = 1024) //Kilo Bytes            {                Decimal FileSize = Decimal.Divide(TotalBytes, 1024);                return String.Format("{0:##.##} KB", FileSize);            }            else if (TotalBytes  0 & TotalBytes              {                Decimal FileSize = TotalBytes;                return String.Format("{0:##.##} Bytes", FileSize);            }            else            {                return "0 Bytes";            }        }        private void button1_Click(object sender, EventArgs e)        {            // The name of the file            const string FileName = "C:\INSTALL.LOG";            // Create new FileInfo object and get the Length.            FileInfo fInfo = new FileInfo(FileName);            long Result = fInfo.Length;            //Display In Label            label1.Text = GetFileSizeInBytes(Result);        }    }}