The combat calculator is a tool to see how many levels you need to gain in order to get a combat level.
To start, you can either enter your RuneScape name or your current levels in their respective fields. If you enter your RuneScape name, your stats will be retrieved from the RuneScape hiscores. Missing stats will be displayed as 1, so you will have to set it to your correct level manually.
Tip: If you are a member and wish to see your combat level on a free world, set your summoning level to 1.