The following pages illustrate locomotive dimensions that I have obtained either indirectly (from specifications or online measurement sources) or directly (by measuring locomotives myself). Where applicable, these dimensions are also listed in the pages of Locomotive Phases.
While all the drawings in the 1:18 series require (at a bare minimum) official length/height/wheelbase dimensions to work from, any and all unknown dimensions (such as hood doors, bolt spacing and intakes) are scaled using photos and proportioned according to known dimensions. While this method provides accuracy to within a fraction of an inch, I don't list these dimensions because the measurement method is still indirect. This method has, however, occasionally revealed errors in the dimensions listed by the locomotive manufacturers.
Drawings with dimensions listed
Drawing Scale and Measuring
The number listed for the drawings (1:36, 1:18 and so on) ultimately has little meaning on the screen beyond establishing the relative size of the drawings - because different monitors have different pixel resolutions. The drawings are scaled at a fixed pixel-per-inch ratio, and the scale is based on a print resolution of 72 PPI. This is to maintain consistency with other drawings on the web (such as the Railroad Paintshop) which are often scaled based on a 72 PPI resolution. In terms of the actual size of the drawings, the 1:36 and 1:18 series are drawn at 2 and 4 pixels per scale inch respectively, so at a given printing resolution, they are exactly 1:(PPI/2) and 1:(PPI/4) respectively.
Obtaining dimensions from the images
For drawings in which I haven't listed dimensions, given the fixed pixel-per-inch ratio of the drawings, obtaining dimensions from the 1:36 and 1:18 drawings is very simple:
- 1:36: Divide the image dimensions by 2 (for inches) or by 24 (for feet)
- 1:18: Divide the image dimensions by 4 (for inches) or by 48 (for feet)
The 1:55 drawings use a more obscure number for the scale - 16.2 pixels per foot - and frankly, many of them (at least the older ones) aren't worth measuring.
To obtain a dimension from within one of the drawings, use a selection tool that displays the selection dimension in pixels, and overlap only one of the two lines to account for the line width. The example below shows a measurement of the first hood door on a 1:18 EMD GP38-2 drawing at 400% zoom. The selection indicates a width of 73 pixels, or a scale width of 18.25". (The door is nominally 18" wide, with a 0.25" gap.)