Scaling targets

Math is like going to the gym for your brain. It sharpens your mind.

Danica McKellar

“Claude, how do I shrink an IDPA target so it appears as though it is 25 yards away when my dry fire range is 7 yards? Thank you.”

Many people think they will never use elementary algebra once they leave high school but sometimes it still comes in handy. The above question can be simply solved through the use of cross-multiplication.

The first part of the problem is we have to determine the ratio of the two distances and then solve for the correct size (height) of the target. The IDPA target is 30 inches tall and would be full size at 25 yards. How tall would it be at seven yards?

Height 30 x
yards 25 7

Cross multiplication means the product of the upper left and lower right will be the same as the product of the lower left and upper right. So, 30 times 7 will equal 25 times x. This works out to 210 equals 25x. But we only want 1x, so we then divide both sides by 25. Our answer is 8.4. I.e., a target 8.4 inches tall at seven yards will have the same size ratio as a full size (30 inch) target at 25 yards. Granted, there are depth perception and visual acuity issues that come into play but it’s an imperfect world and we just do the best we can.

The second part of the problem is to make a target 8.4 inches tall out of the images available to us. I did this using crude methods but effective. Using an IDPA target image captured from the internet, I sent it to Print Preview.

IDPA target

The original size was way too small so I took a guess and enlarged it to 400 percent. I then took a ruler and measured the preview pane, which was 2.25 inches tall. This makes a relationship of 2.25 inches to an actual print page of 11 inches. The target image height is 8.4 inches so the task is to find the representative size on the screen. Cross multiples again can provide the answer.

Actual height 11 8.4
Screen height 2.25 x

This gives us 2.25 times 8.4 equal 11x. 18.816 equal 11x. 18.816 divided by 11 gives us 1.72, the desired screen height. However, the 400 percent image on the screen only measured 1.375, so I needed to find the correct print percentage. Doing another cross-multiplication answers that question.

Screen height 1.375 400
Desired height 1.72 x

Solving for x gives 500 percent, which I then printed and verified.

Since I do this regularly, I have a scaling spreadsheet set up in Excel. It allows me to do this kind of scaling in less time than it probably takes to read this post.

IDPA target 7-25

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One response

  1. Ben Stoeger pro shop offers many different varieties of precut scaled dry fire targets. http://www.benstoegerproshop.com/Build-Your-Own-Scaled-Dryfire-Target-Kit-p/byo-df-kit.htm

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