- Leder is a neuter noun
- This is nominative case
- There is no preceding article (das, ein) which means we should use strong declension
Looking at this strong declension table http://en.wikipedia.org/wiki/German_declension#Strong_inflection.5B6.5D.5B7.5D
under neuter and nominative, we see that the ending used is -es.
For wiki pages, click on the desired section in the "Contents" table at the top of the page. Then copy the url.
- Go here: http://en.wikipedia.org/wiki/German_declension
- scroll down a little to the "Contents"
- click on desired heading
- that takes you to the section (I chose "Strong inflection")
- copy url http://en.wikipedia.org/wiki/German_declension#Strong_inflection.5B6.5D.5B7.5D
To add to Hohenems' good answer, if you don't like memorising tables you can perhaps memorise the flow chart style questions outlined here:
http://www.nthuleen.com/teach/grammar/adjektivendungenexpl.html (I didn't find this link btw, it's from another Duo user's comment )
cool algorithm, only 1) its language is horrid. Instead of the 'original, unchanged, standard'' form it should use 'nominative' form and instead of 'its der-word ending' should be 'ending of its definite article'. 2) the algorithm errs in the endings of genitive case without article where it suggests: M -en N -er F-en P -er yet correct is M -es F -er N -es P -er
Please tell me if my simplistic method is functional or have I just been luck. If I see a noun without an article I use the ending that would have been on the article. E.g 'Leder' is neutral, 'das Leder', so in place of 'das' I put 'rotes' to get that "s" in. Of course that's assuming I know the gender :-(.