Having blueprints, plans or photos scaled properly to N scale can be very helpful whether you’re scratchbuilding or just want a scale reference. For many modelers, sizing a photo or plan can be intimidating and raises many questions. I’ve personally spent hours on Google over the years searching for “N scale plans” or “N scale blueprints” before I realized how easy this can be, without the need for commercial software.

I’ll show you how to quickly and easily size a photo or plan to N scale — or any scale for that matter. This won’t get you CAD-quality plans to work with, but it will give you something that can easily act as a guide. I’ve followed this exact method when I sized blueprints I found on the Internet for my scratch built IRT Subway Kiosk project.

Percentage Calculation

We are used to working with one very basic calculation — 1/160, which is technically the protoype size divided by 160 to convert from prototype size to N scale. And of course, the referse of that, prototype size times 160 to convert from N scale to prototype size. Almost every N scale modeler knows this calculation without even thinking about.

But when dealing with computers, it’s much easier to work with percentage values since you can specify percentage in printer options and photo editing software. So, we’ll be using a formula that is much more complex then 1/160 but still fairly easy to use. Let’s get familiar with it.

The Formula

The formula for scaling photos is: (((Scale Inches - Printed Inches) / Printed Inches) * 100) + 100 = Print Percentage

Let’s take a look at how to use it.

Print the Prototype Photo and Measure

Before you do anything, print the prototype photo you have without changing anything. Print it at 100% in your printer settings, even if the photo is cut off the paper.

For this method to work, you’ll need to be able to estimate the real-life (1:1) measurement of an object in the photograph. You’ll want to look for objects in the photo print out that are familiar and have common sizes. For example, the width or height of a door, the size of a commercial sign that may have be standard for a chain business or a fixture like a fire hydrant that you may be able to find size estimates by searching the Web. Once you choose an object to use and guestimate it’s real-life (1:1) size in inches, divide it by 160 in order to convert it to N Scale. This number is your SCALE INCHES. The way to remember that is the size of the object in “N SCALE INCHES“. This is basically the size you want the object to be on your model, in N scale.

Then, using the photo you printed, meausre the same object directly on the print out. It’s best if you can use a digital caliper to get decimal inches. If you don’t have a caliper, you can convert fractional inches to decimal inches manually or by using an online calculator. Alternatively, you can measure it in millimeters and convert the millimeter measurement to decimal inches or measure it on screen with photo editing software.

We’re just looking for the size of the object on the printout. In the forumula, this number will be your PRINTED INCHES.

Example

Once you have those two numbers, you just need to plug them into the formula.

Let’s say you printed your photo (at 100%) and you find a door in the photo. You belive the door to be 36″ wide on the prototype. Divide 36″ by 160 to convert it to N scale (0.225). 0.225 is your SCALE INCHES.

Then, measure it on the printout and let’s say it’s 3/16″ or .1875″. Then .1875 is your PRINTED INCHES number.

Plugging that into the formula, (((Scale Inches - Printed Inches) / Printed Inches) * 100) + 100 = Print Percentage, this example would be:

(((0.225 - .1875) / .1875) * 100) + 100 = 120%

Following basic mathematic guidelines, you’d do 0.225 minus .1875 first, which equals 0.0375. Then divide that by .1875 which equals 0.2. Multiply that by 100 to get an answer of 20. Add 100 and your final answer is 120.

How to Print Your Photo in N Scale

In the above example, 120 is your PRINT PERCENTAGE. What that means is that if you reprint your photo and change your printer settings to scale to 120%, your photo will be scaled to N scale. It’s really as simple as that.

This formula will work in all instances. In the example, I used a photo that needed to be enlarged to be converted to N scale but this will work even if your photo needs to be reduced in size. Reducing is probably more likely, but the formula always remains the same.

Adjusting Your Measurements

Sizing photos using this formula doesn’t really require that you get all of the measurements exactly right the first time. Sometimes, this approach will get you very, very close but you may still need to adjust.

When you reprint your photo with the new percentage, measure the same object on the new printout with a scale ruler. Is it what you expected? If not, you can adjust by changing the print percentage slightly — by 1% or less in some cases — until you get it just right.