I wanted to pay around with the lulu page sizes for printing, so I made some css variables out of their product page: https://xpress.lulu.com/our-products

luluBookSizes.css

:root { 
    /* Lulu Book Sizes */ 
    --US-Trade:            6in     9in;     /* The most common size for trade paperbacks and hardcovers, used primarily for fiction but well suited for a variety of book designs. */
    --US-Letter:           8.5in   11in;    /* Used for hardcover books, manuals, and other large size works, US letter is a great option for image-heavy books. */
    --Digest:              5.5in   8.5in;   /* A smaller trade size, digest is one of the most commonly used sizes for fiction and nonfiction works. */
    --Executive:           7in     10in;    /* Executive size fits between US trade and US letter and is commonly used for journals and graphic novels. */
    --A5:                  5.83in  8.27in;  /* Standard size for international trade paperbacks and hardcovers. Similar to US trade size but slightly smaller. */
    --A4:                  8.27in  11.69in; /* A4 is the standard size used for many magazines and catalogs. */
    --Royal:               6.14in  9.21in;  /* Royal is slightly larger than US trade, and works well for the same fiction and nonfiction content. */
    --Crown-Quarto:        7.44in  9.68in;  /* Crown quarto provides a wider page than US trade, and is perfect for a book with two-column printing. */
    --Square:              8.5in   8.5in;   /* Square format best for accommodating full-bleed images without constraints on landscape or portrait formatting. */
    --Small-Square:        7.5in   7.5in;   /* Small square is perfect for image-heavy content, such as a travel book, children’s book, or memory book. */
    --Pocket-Book:         4.25in  6.875in; /* The smallest Lulu format, used for fiction as well as references and poetry collections. */
    --US-Letter-Landscape: 11in    8.5in;   /* US letter size in landscape format, great for children's books or photo books. */
    --A4-Landscape:        11.69in 8.27in;  /* Common internationally, A4 landscape is perfect for photo books or art books. */
    --Small-Landscape:     9in     7in;     /* Small landscape is ideal for photo books and product guides meant to highlight images and photos. */
    --Calendar:            11in    8.5in;   /* Standard landscape size with Wire-O binding along the edge and a punch hole for hanging. Used only for Calendars. */
    --Comic-Book:          6.63in  10.25in; /* Unique book size used for our traditional comic book printing. */
}