Okay, try this. A 14 inch circle (radius of 7 inches) has an area of 154 square inches. If your original recipe calls for a 9 inch circular pan (radius of 4.5 inches), that 9 inch circle has an area of 63 inches.
So, if the original recipe was also for a 4 inch tall cake 9 inches across, you need just under 2-1/2 times the original. Use 2-1/2, and you'll be certain to have enough. If the recipe was for a 2-inch tall cake, you would need twice that, or 5 times the recipe.
Most cake recipes scale alright. (Not bread and other yeast recipes. There are special considerations for them.) But you also have to think about baking time and temperature. This will be most critical if your recipe is designed for, say, 2-inch tall pans, and you want to bake it in a single 4-inch tall pan. You get into a problem of area/volume ratio. And it's further complicated by the fact that a large part of the batter is within the pan. Best to test by temperature or toothpick to test interior doneness. And be prepared to protect the open top with foil, if it gets too brown before the interior is done.
If I guessed wrong about the original 9-inch, and you have trouble adapting from some different size, post whatever the recipe is for, and I or someone will recalculate.
"Kitchen duty is awarded only to those of manifest excellence..." - The Master, Dogen