[c#] How to open new browser window on button click event?

You can use some code like this, you can adjust a height and width as per your need

    protected void button_Click(object sender, EventArgs e)
    {
        // open a pop up window at the center of the page.
        ScriptManager.RegisterStartupScript(this, typeof(string), "OPEN_WINDOW", "var Mleft = (screen.width/2)-(760/2);var Mtop = (screen.height/2)-(700/2);window.open( 'your_page.aspx', null, 'height=700,width=760,status=yes,toolbar=no,scrollbars=yes,menubar=no,location=no,top=\'+Mtop+\', left=\'+Mleft+\'' );", true);
    }