Dee, There are some holes in your question, which makes it a bit tricky to answer ... 40 square feet is definitely an area but you are probably going to have to cut tiles so having more detail on your area might help (eg. maybe splashback 5 tiles high). You gave dimensions for tiles as 10 by 28. 10 by 28 what? If I assume inches then area of a tile is 280square inches. Total area is 40 square feet = 230400 square inches. 230400/280 = 822.9 ... so possibly you need at least 823 tiles
