The truth is, there is no perfect formula or ratio for what will sell in your area. Yes there are general guide lines which well talk about shortly, but the only real way to find out is to just get out there and start pushing your product. Talk with your customers, gauge their interests. See what they are looking for or expect from you as their supplier.
We've spoken with customers in Florida who sell bath bombs in tourist areas. They tend to have higher sales of tropical fragrances. Which makes sense right? You'd expect a tourist shop on a beach to do well selling coconut scented items. In contrast, they sell way less patchouli scented items compared to a store in Michigan. Citrus, sweet, floral, and coconut are great for certain markets, while a ranch in Montana might do better selling earthy, green, natural scented products.
So with your location in mind, the next thing to is make sure you're covering all of your major fragrance groups. At least initially until you have a better idea of what is selling in your area. A common question we get goes something like, "Hey, this is my first order what fragrances do you recommend?". We always advise on an assortment of the best selling fragrances. This way you are able to offer a wide variety of scents knowing these are the items moving for other business owners. You can always adjust the fragrances you offer later.
Let's say you have a pretty good idea of what will move for you. We still recommend covering the major scent categories. What you need is a solid green floral/herb (patchouli, sandalwood, rosemary etc.), sweet floral (hibiscus, plumeria, violets etc.), fruit, mint, and a unisex fragrance. Other fragrances that are extremely popular for us are Lavender, Vanilla, Orange, Almond, and Coconut. If you only had those 5 you'd still be in pretty good shape. Everyone knows what they smell like, they are universally popular, and they have been around for literally thousands of years!
Try not to over complicate it. Offer your customers a wide variety of popular, best selling fragrances and make adjustments as you go. Remember, just because YOU may like a certain bath bomb scent, doesn't mean it will sell well.