How to convert my IGCSE grade to Gpa?

So i tried converting my IGCSE grade to Gpa but this website didn't give me my gpa just gave me the USA grade. I tried to average this and get my gpa but I am not 100% sure if that is the right method. Can sm pls help?

So i tried converting my IGCSE grade to Gpa but this website didn't give me my gpa just gave me the USA grade. I tried to average this and get my gpa but I am not 100% sure if that is the right method. Can sm pls help?