To check your chain for wear, measure it with a tape measure, scale or what have you.
The longer the length you can measure, the better resolution.
I can only handle a 3' long piece without feeling I might compromise accuracy.
IF you have a helper, measure a 5' section.
Chain wear is measured in a %.

Per Sheldon RIP-
https://www.sheldonbrown.com/chain-wear.html

• If the link pin is less than 1/16" past the mark, all is well.
• If the link pin is 1/16" past the mark, you should replace the chain, but the sprockets are probably undamaged.
• If the link pin is 1/8" past the mark, you have left it too long, and the sprockets (at least the favorite ones) will be too badly worn. If you replace a chain at the 1/8" point, without replacing the sprockets, it may run OK and not skip, but the worn sprockets will cause the new chain to wear much faster than it should, until it catches up with the wear state of the sprockets.
• If the link pin is past the 1/8" mark, a new chain will almost certainly skip on the worn sprockets, especially the smaller ones.

Translate mark to 1 foot.