It is helpful to use this cheat sheet from Infographicjournal.com though I seriously doubt I will be worrying about the sizes of the posts and other images, especially because of FB's penchant for changing their layouts and sizes of everything. All the time.
However, what I would recommend, is that when designing your header you work in a proportionately larger size. For instance I make the header box 851px x 315px, but I work in 300 dpi. (Sometimes I even proportionally scale the pixel size.) This creates a better looking, sharper image, (especially if you use type) when it's uploaded to FB.
Here's another hint: I save a layered version of this so that when I want to change the image or type, I just create a layer for the new image.
Here's the result on my Mermaid Sue's Studio Facebook page:
It's also good to know that Facebook has rules about what can be in that header image. (I was looking for the link - but they do make it rather hard to find stuff sometimes. Sigh.) How much type you're allowed to have (20%), no advertising (20% OFF!), no calls to action (LIKE THIS PAGE!).
(The Blue Truck, North Fork painting above is no longer for sale - It IS however, available as a print on Fine Art America.)
Which brings us to something else blue:
((See how I did that?)
On My Night Table - Sacré Bleu a Comedy d’Art by Christopher Moore
It is July of 1890 and Vincent van Gogh has shot himself...or has he?
I'm about halfway through right now – it takes me forever to finish anything. I never quite get the time to read more than 10 pages at a time and it's always right before going to sleep. I'll let you know how it turns out!