Get the ratio of the areas of the pans, then use that ratio to scale the ingredients.

let's say orig recipe says:

11x17 pan

342 g flour

if you have a 9x8 pan, the ratio of pan sizes is:

(9x8)/(11x17) = 72/187 = 0.3850 or 0.39

So multiply the orig amount of flour by 0.39:

You will need 342 x 0.39 = 133.38 or 133 g flour (I round flour to the nearest whole number grams)

if you have a 14" round pan, you get its area (pi x radius squared):

3.14 x 7x7 = 153.86 or 153.9

Make your ratio: 153.9/187 (area of your pan / area of orig recipe) = 0.82299 or 0.83

Use that ratio to calculate the new flour amount:

342 x 0.83 = 283.86 or 284 g flour

For a reality check, be sure that if your pan is smaller, you are using less flour, and vice versa if your pan is larger than the original