A pea size for any skin type is enough!
Oily skin type: a pea size is just right, apply alone as your main moisturizer or over a mattyfying primer.
Dry skin type: apply over a serum or your regular moisturizer.
Combo skin types: apply a moisturizer in your dry areas only.
BB creams are not meant to mask, completely conceal, or hide imperfections. They are a tinted moisturizer with added benefits. Although some are more pigmented and provide slightly more coverage they are not in any means a medium to full coverage foundation. The great thing about BB creams is that they even out your skin tone by not having to wear a foundation. If more coverage is needed I suggest you either spot the area with either concealer or a medium to full foundation. Powder foundation is another great option over top for added coverage. By adding more than a pea-size amount you risk getting oily, streaky, and unevenness.
Do you use BB Creams? Or do you continue to use Foundations?