Duplicate Sheet

use this code

Dim a, b, sel_rg
Sheet1.Activate
a = Cells(1, Columns.Count).End(xlToLeft).Column
b = Cells(Rows.Count, 1).End(xlUp).Row
sel_rg = "A1:" & Cells(1, a) & b
    Range(sel_rg).Select
    Selection.Copy
    Sheets("Sheet3").Select
    Range("A1").Select
    ActiveSheet.Paste