Fine vs Medium Ballast

The stones under a real railroad are a fixed real world size, typically one to two inches across for mainline ballast. Once you pick a scale, that real size has to shrink by the scale's proportion, so HO's 1:87.1 ratio needs visibly finer grains than a full size photo would suggest, and N scale's 1:160 ratio needs finer grains again. Medium ballast, correctly scaled for HO, is roughly twice the apparent size of fine ballast scaled for N. Put medium grade under N scale track and the individual stones look too large relative to the rail and ties, an effect the eye reads instantly as riprap or gravel rather than ballast, even before you consciously compare the two.

Yes, and this is where the mistake most often happens in reverse: modelers moving from HO to O gauge sometimes keep buying medium ballast out of habit, when Woodland Scenics B89 Coarse Ballast Bag Gray 18 cubic inches is the grade actually scaled correctly for O and larger. The rule of thumb is straightforward: fine for N, medium for HO, coarse for O. It is a rule of thumb rather than a hard standard, and a manufacturer's own recommendation for a specific product line should win if one is published, but it holds for the overwhelming majority of layouts.

Grade decides whether the ballast looks like the right scale, and color decides whether it looks like the right railroad. A clean gray like Woodland Scenics Fine Ballast Shaker Gray 50 cubic inches or Woodland Scenics Medium Ballast Shaker Gray 50 cubic inches suits a well maintained modern mainline. A blend like Woodland Scenics Fine Ballast Shaker Gray Blend 57.7 cubic inches breaks up the flat single tone that a pure gray shaker leaves behind, which reads better under most layout lighting. Woodland Scenics Brown Ballast 32 oz Shaker suits a branch line, a yard, or an older right of way where dirt and cinders have taken over from clean stone, and Woodland Scenics Fine Ballast Shaker Buff 57.7 cubic inches suits a western or desert prototype where the local rock is not gray granite at all.

More than the first estimate, almost every time. Ballast has to cover the shoulder on both sides of the ties as well as the space between the rails, and a shaker bottle empties faster than it looks like it should once you are working a full mainline rather than a test section. Rather than guess and reorder twice, run your actual track footage and scale through the ballast and scenery calculator, and see the full lineup of grades and colors at best model railroad ballast.