Hi Bren, it's difficult to give you a one-size-fits-all ratio for increasing bread and pound cake recipes that are written for smaller pans to fit your 13" pain de mie, but a rough rule of thumb would be to multiply the weight of each ingredient by 1.45. In the case of yeast breads, however, you may not want to increase the yeast amount, and just allow for slightly longer rise times. 

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