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Scale Drawings Conversion Chart

n by Martin Waligorski



Like many modellers, every once in a while I work from scale drawings. The drawings are most effective when printed in the exact scale of the model. If done so, they can be used directly for dimensional measurements by laying the model parts on top of the drawings. They can also be used to check the outline accuracy of the parts. Or to cut masks for camouflage designs or markings. 

On the contrary, having even the most detailed drawing in a wrong scale is much less useful since it can only serve as a general reference.

Back in the 1970s when advanced photocopiers were still something of a luxury for the few, this was a major problem. Nowadays, all you have to do is to get your hands on the nearest copier, enter the appropriate enlargement/reduction ratio, and press the Copy button.

But... what was that correct reduction rate for your scale...? Yeah, I remember... it should be easy to calculate... yeah...you divide this by that, or was it the reverse...I'm not sure.... help!

Having done and forgotten the maths a couple of dozen times, I created a scale conversion table that takes the thinking out of the process. You can consult it for the accurate enlargement/reduction rate between any two of the popular aircraft, armour, railroad and car scales. I have it printed in my drawer and take it with me whenever I intend to copy some scale drawings.

The rates are given in percent, which is common scaling notation for photocopiers throughout the world. As they are also rounded off to a full percent, all you need to do is enter a given value on the photocopier and start copying.

To scale         Reduce
From 1:16 1:24 1:25 1:32 1:35 1:48 1:50 1:72 1:76 1:87 1:100 1:144 1:160
1:16   67% 64% 50% 46% 33% 32% 22% 21% 18% 16% 11% 10%
1:24 150%   96% 75% 69% 50% 48% 33% 32% 28% 24% 17% 15%
1:25 156% 104%   78% 71% 52% 50% 35% 33% 29% 25% 17% 16%
1:32 200% 133% 128%   91% 67% 64% 44% 42% 37% 32% 22% 20%
1:35 219% 146% 140% 109%   73% 70% 49% 46% 40% 35% 24% 22%
1:48 300% 200% 192% 150% 137%   96% 67% 63% 55% 48% 33% 30%
1:50 313% 208% 200% 156% 143% 104%   69% 66% 57% 50% 35% 31%
1:72 450% 300% 288% 225% 206% 150% 144%   95% 83% 72% 50% 45%
1:76 475% 317% 304% 238% 217% 158% 152% 106%   87% 76% 53% 48%
1:87 544% 363% 348% 272% 249% 181% 174% 121% 114%   87% 60% 54%
1:100 625% 417% 400% 313% 286% 208% 200% 139% 132% 115%   69% 63%
1:144 900% 600% 576% 450% 411% 300% 288% 200% 189% 166% 144%   90%
1:160 1000% 667% 640% 500% 457% 333% 320% 222% 211% 184% 160% 111%  
Enlarge            

How to use the table

Suppose that you need a scratchbuild city house for a 1:35 armour diorama. You find a drawing of an appropriate house in a railroad magazine, printed in the HO scale, corresponding to 1:87. The drawing is much smaller  than the intended house model. Here is how to find an appropriate enlargement rate.

In the leftmost "From" column of the table, locate the row representing the initial scale of your drawing. This is 1:87, located in the 10th row counting from the top. 

Having located the appropriate row, forget the rest of the table. You will only need that row.

Now, move your finger to the right along the row, locating the column corresponding to the scale that you'd like to convert to. In your case it is 1:35, the 5th column counting from the right.

Read the percent value in the located cell - in your case it should be "249%". Set your copier to 249% enlargement and copy the drawings. Ready!

n


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