How many gingerbread cookies per batch

Rolled area is the dough volume divided by the thickness. The dough volume is its weight divided by a density of 1.2 g per cm³, the same figure the dough guide uses for houses. Cookies are the rolled area, times the share of it you can use, divided by the area of one cutter.

Three numbers are my assumptions, not published figures. First, the share of dough that ends up in a cookie on one pass: 65% for round cutters and 60% for gingerbread men, because gaps between cutters and the trimmed edge are lost. Second, a re-roll cuts the scraps once more at the same share, so the total is 1 - (1 - share)². Third, a gingerbread man cutter covers 30% of its height squared, which makes a 4 in man about 4.8 in². Cutters differ a lot here, so measure yours if you can.

For "my own dough by cups of flour", the page multiplies the flour by 290 g of finished dough per cup. I got that from the three recipes below, whose dough comes to 288 to 294 g per cup of flour.

I opened each recipe and added up its ingredients to get the weight of the dough (a large egg as 50 g, spices and leaveners as a few grams, so these are rounded). Then I ran each one at its own thickness and cutter, with one re-roll.

King Arthur Gingerbread Cookies gives a range of thicknesses (1/8 to 1/4 in), so the estimate is a range too, and the stated 36 to 42 cookies sit inside it. Taste of Home Gingerbread People comes to 31 against its stated 30. I set the gingerbread man area after looking at that number, so it is not an independent test.

RecipeTin Eats Gingerbread Men is where the estimate fails: it gives 38 cookies for a stated 18 to 20. The recipe rolls thin (4 mm) with a 4.5 in cutter, so either that cutter is chunkier than my shape, or the cookies are cut with less re-rolling than I assume. If your cutter is wide and thick-limbed, expect fewer cookies than the page shows.

With the dough you entered (870 g), 1/4 in thick and one re-roll:

Halving the cutter width roughly quadruples the count, since the area goes with the square. Thickness works the other way: the same round cutter of 3.0 in gives 43 cookies at 1/8 in, 29 cookies at 3/16 in, and 21 cookies at 1/4 in. Thin cookies bake crisp and thick ones stay soft, and King Arthur says the thinner you roll, the crispier the cookies.