How are speaker sizes measured?

I am replacing boat speakers, how are they measured? The holes cut are 5-1/4″, mounting screws at 5-1/2″ and the speaker itself appears to be about 4-1/2″.

Any ideas?

My guess is 5-1/4″, because 5-1/4″ and 6-1/2″ seem like popular sizes.

I read on and my guess was wrong, shocker.

6-1/2″ 2-Way Coaxial Marine Speakers with Polypropylene Cones (Pair) 5-1/2″ round cutout diameter

IIRC speake size is the size of the speak, not including the metal housing on the outside, so I’d guess and say you have 4.5 inch speakers. Crutchfield used to give speaker dimensions in their catalogs, I supect they still do online, its probably a bit harder to compare mulitple speakers online.

If you can find any model number or anything on your current speakers, google the numbers you may be able to find out some more info.

Just because they are 4.5 inch speakers doesnt mean any 4.5 will fit so be cautious, depth is usually more with better speakers…

Your correct Nick, better speakers have larger magnets and require more depth. Depth is not an issue luckily. I am looking at some economical Boss and Pyle marine speakers. Thanks for the info.