Average Size Main Drain Cover

[pooly1]

Is there a Average Size Main Drain cover? I need to replace mine, but I wanted to order the new one first. Its a round one.
Heres a bad pic but maybe someone would have a good idea

 

[JasonLion]

They come in many different sizes and screw hole configurations. The replacement needs to match very closely. You will probably need to remove the old one and examine it above water for a part number before you can order the correct replacement.

You should also check that the drain design and new cover meet the new legal requirements for anti-entrapment. If that is one of a pair of connected drains this will be easy, but if that is a single drain there may be additional complications.