Plans in model railroad books and magazines are often in a different scale from your favorite. Having aÂ model railroad scale conversion chart helps.

I’m into O scale and the rest of the world, it usually seems, is not. Dimensions for published plans are almost always sized to HO scale, or even S scale of all things. Of course, after A. C. Gilbert imploded in 1967 and took American Flyer with it, it seemed like the “S” is S scale stood for “scratchbuild,” because building it yourself was the only way you were going to get anything, so I guess that’s fair.

Here’s a cheatsheet you can use to convert measurements from one scale to another.

Assumptions: O scale is 1:48, G scale is 1:22.5. If you use a different measurement for either scale, I’m sorry. This won’t be much use to you.

 G Scale O Scale S Scale OO Scale HO Scale TT Scale N Scale Z Scale G Scale 213% 284% 339% 386% 533% 711% 977% O Scale 47% 133% 158% 181% 250% 333% 458% S Scale 35% 75% 119% 136% 188% 211% 289% OO Scale 30% 63% 84% 115% 158% 211% 289% HO Scale 26% 55% 73% 87% 138% 184% 253% TT Scale 19% 40% 53% 63% 73% 133% 183% N Scale 14% 30% 40% 48% 54% 75% 138% Z Scale 10% 22% 29% 35% 40% 55% 73%

Find your scale in the table along the top. Then scroll down to the desired scale and find out the factor you need to enlarge or reduce. So, if, say, I have HO scale plans I want to enlarge to O scale, I run across the top to HO, then down to O scale, and see that I need to enlarge the plans to 181%. If I have O scale plans I want to reduce to S scale, I run across the top to O and down to S, and see I need to reduce the plans to 75%.

You can also do this if a building you want exists in kit form for a different scale. Measure it. Then do the math based on the chart to figure out what size to build everything for your scale of choice.