How much storage space do you have? How frequently do you want to do laundry? How much variety do you want in your wardrobe? People notice tops more than jeans, unless they are some sort of Statement item. That allows for many fewer jeans in a most people's wardrobes than tops, even if they are frequent denim wearers. Do you wear jeans to work? To the park? To do the gardening? To the grocery store? These may all be slightly different styles, Kwim?
I once found a formula to help figure out the number of various articles of clothing I might need, but you can easily come up with your own calculation. In my case, my closet is large, my lifestyle is jeans friendly, and I have lots of them (as many people on YLF already know ).
How often do you want to repeat wears of your clothes, and what activities do you need to dress for? How much value do you want to get from each item of clothing (cost per wear)? I think these are all helpful questions when sorting out wardrobe size. I once made an arbitrary decision not to repeat wears of my outfits for a three week period. That means I would go almost an entire month and never wear the same thing twice. In a season, which lasts six months (I lump Spring/Summer and Fall/Winter together), I might only wear something six to eight times. This might not be a desirable repetition ratio for most people. I don't think I make purchases and say to myself, I will only wear this item 6 times this year. If I increased my outfit repetition frequency to every two weeks, I almost double the wear I get from each item in any given season. It sounds a lot better to me to say I will wear something 12 times in the year I purchase it, especially if it isn't a special occasion item. In any case, thinking this through, can help you sort out some numbers.
(Truth time: I have over 20 pairs of jeans, and most people here on the forum are probably laughing as they read that I am talking about cost per wear and value from clothing, but it is my year of being budget conscious, so I have been just that! )