Roofing Nails are used to attach shingles to sheathing on a roof. There are two densities used for the number of nails needed per shingle. This can be seen in the shingle diagram to the right. One image shows four nails per shingle above the tab cuts. This is for normal wind conditions. The second image shows six nails per single with a double nail above the two central tab cuts. This is for high wind conditions on places like on the edge of bodies of water or other exposed places with no wind breaks. High winds are experienced in areas with little cover from wind breaks. Such areas include deserts, prairies, mountain tops and areas adjacent to large bodies of water. High winds are also associated with areas prone to hurricanes.
Note that for both normal and high wind applications, the roofing nails go just below the sealant strip.
Roofing nails are sold by weight in many places. The weight of the nails is based on a 5lb box of 1-1/4" smooth shank nails having 978 nails. That's 0.0818 ounces per nail.