Mentioned in Lemon and Poppy Seed Cake - Helen Goh - https://food52.com/blog...
King Arthur Flour says 8.5x4.5" (this holds about 6 cups)
Others say 9x5" (about 8 cups) or call this a large standard.
Either will give you good results.
But much smaller or larger than this will need adjustments to the recipe.
The pan sizes are precisely described in the headnote of the actual recipe:
I'm obviously missing something, I do not see any measurements on the page, but found the answer at another site, Thank you.
Read the recipe headnote (labeled as "Author's Note") and click the hyperlink "(...more)" after the "However ambitious and di" sentence fragment.
That will fully expand the headnote (it's long).
You can make this in a standard 8 1/2 x 4 1/3-inch/900-g loaf pan, as we do here, or, if you have them, nine mini-loaf pans (3 1/2 x 2 1/3 x 1 1/2 inches/9 x 6 x 4 cm) also work well. If you are making the mini loaves, shorten the baking time to 25 minutes."
Note: many recipes on this site and others have headnotes which often contain valuable insight or additional notes beyond the step-by-step instructions.
Best of luck.