A simple method for converting scales

Often times, model ship builders build their models from blueprints of the actual ship. Other times they just wish to build a different size ship, be it bigger or smaller from the plans they have. Regardless of the reason they have, it's necessary for them to understand how to re-scale the information on thier drawings.

As a novice modeler, I had a hard time learning this "scale" thing. I knew that I either liked the size of a model I was looking at or was wondering, just how could I make it bigger??? or smaller??? Just, what's the science to it all????

Well, once I figured it out I was quite disappointed with myself. It was no where's near as hard as I thought. But then I've always liked making mountains from mole hills (ha-ha).

There are some simple methods used in redrawing plans. One of the most common is using a photo-copying service. You simply bring in your plans and tell them how much bigger or smaller you want the drawings to be.

For example if you wish to have your drawings converted from a 1/4" scale to 3/16" scale, you can ask the copying service to reduce the drawings by 25%.

The equation for converting from one scale to another is:

TS = FS x CM


  • TS = Dimension in the "to scale", or the scale you want to convert your drawings to.
  • FS = Dimension in the "from scale", or the scale your drawings are now.
  • CM = Conversion multiplier

The following table lists various common conversion multipliers:


From To 1/8 To 3/16 To 1/4
1/16 2.0 3.0 4.0
1/12 1.5 2.25 3.0
3/32 1.33 2.0 2.67
1/8 1.0 1.5 2.0
5/32 0.8 1.2 1.6
3/16 0.67 1.0 1.33
1/5 0.625 0.94 1.25
7/32 0.57 0.86 1.14
1/4 0.5 0.75 1.0
1/2 0.25 0.375 0.5


(The formula for calculating the Conversion Multiplier is: Conversion Multiplier = TS / FS)

To simplify matters even more in your conversion, consider, if you're not already doing this, using metric measurements. While scales are expressed in fractions, fractions in the old English measurement system complicate matters even more. Where as, the metric system works on the base 10 system which we are more familiar with when dealing with numbers (i.e. 1 meter = 100 cm = 1000 mm).

For example

Let's say we have a component that is 1" in length on the draft using the 1/4" scale. Using a metric ruler we find that it is 25.4mm in length. To convert to the 3/16" we determine the conversion multiplier, which in this case is 0.75 and apply it to our formula

TS length = 25.4mm x 0.75

TS = 19.05mm or simply 19mm

Either way you decide to do your conversion, I hope that this short article helps make the process simpler.


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