The major variables of reproductive output and fecundity were compared among brooding females of nine species of Cancer from the North Pacific and North Atlantic: C. oregonensis, C. gracilis, C. irroratus, C. antennarius, C. productus, C. borealis, C. anthonyi, C. magister, and C. pagurus. Female body size is the principal determinant of reproductive output, with dry body weights spanning two orders of magnitude from 1.2 to 199.5 g among species and often one order of magnitude within species. Mean dry brood weights ranged from 0.21 to 26.7 g among species, with relative brood size varying from 11 to 19% of female weight. The brood mass is partitioned into eggs ranging among species from 311 to 442 μm, resulting in mean fecundities ranging among species from 18 200 to 2 208 000 eggs per brood. Most species produce one or two broods per year over the winter–spring season over a reproductive span averaging 6.6 yr (range 4–10 yr). Cumulative reproductive output and cumulative fecundity over the maximum estimated life span exhibited approximately isometric functions of maximum body size, and they ranged among species from 1.88 to 316 g brood weight and 158 000 to 22 300 000 eggs per lifetime, respectively. The pattern of covariation of reproductive traits in the Cancridae corresponds well with the overall pattern previously determined for a diverse array of brachyurans from seven families.