Worn chain?

[dazzawazza]

As a quick test you could measure the length over 12 full links (24 pivots) with a ruler; if you don’t have the tool (metal one better).

If the chain is over 12" 1/16 then it maybe too worn for a new chainring / cassette.

This isn’t an exact science as discussed on various web pages, but should give a good indication if obviously over.

I think hamster has already said using metric

 

[Tall Paul]

A good image if you dont have a chain wear tool:

My chain is much much much worse than that left hand image. It is an SRAM chain, fitted a couple years ago and about 4000 commuter miles under its belt.

New LX cassette and chain on their way.

Nice XT rear mech coming too, to replace the LX item that's done about 30k miles, on the same jockeys....

I should really do some servicing.

 

[RadNomad]

Bear in mind the "chain jumping under load" might actually be the freehub ratchet slipping under load and have nothing whatsoever to do with the state of your chain and rings. Just keep that in the back of your mind in case you still have the "jumping" after installing your new parts.