Space & Science

How to Estimate Distance Using Just Your Thumb

One of the most frustrating hobbies I’ve ever done was archery, but not because it’s hard to hit a target on the wall (it is, but I’m become quite good at it). My problem was that one of the most popular ways to go out and have fun with archery was to do “3D shoots”, where you had to shoot a series of animal statues, each positioned at an unknown distance.

The distance estimate turned out to be my downfall. If you don’t have a good idea of ​​how far away the fake deer is, you’ll end up shooting it or burying your arrow under the ground under its feet. At the time, I assumed that distance estimation was less of a skill to be learned and more of a hunch. Hence my surprise when I recently came across a quick eye and mental math trick which allows anyone to estimate the distance quite accurately.

The technique involves some Gut-level estimation, but a much easier type. Then you simply multiply by 10. Here’s how it works:

  1. Hold your thumb out in front of you (with your arm fully extended) and close one eye. Align your thumb with an object that you know the size of (for example, a car).
  2. Without moving your thumb, close your open eye and open the other. Your thumb will appear to be in a different place.
  1. Estimate the distance your thumb has traveled from the object you are looking at. For example, a car is about 15 feet long, so if your thumb moved half a car length, that’s about 7.5 feet.
  2. Multiply by 10. In this example, you would calculate that the car is approximately 75 feet away from you.

Too good to be true? I walked around and tried. I also took a laser range finder and tape measure with me to check. One thing I noticed right away was that I was tempted to measure the space between my two thumb images; instead, you should measure, for example, from the left side of the first thumb image to the left side of the second thumb image.

Standing in the kitchen, watching the TV in the other room, I thought the TV was about 3-4 feet wide and my thumb was moving just over half its distance, so about 2 feet. Calculation: the television must be 20 feet away. The laser level reads: 25 feet. OK not bad.

From my desk to a nearby bookshelf, my thumb moved 6 inches, maybe a little more. Calculation: 60 inches. Actual measurement: 59 inches.

From a spot in my driveway to a garden shed: I turned my head and to the side to measure the height of the door. The distance between the thumbs should be about 6 feet (most of the door height), so the shed should be 60 feet. Actual measurement: approximately 70 feet. Not perfect, but again, not too far off.

The reason this trick is supposed to work is that the distance between your eye and your thumb is about 10 times the distance from eye to eye. I measured that too. Looking in the mirror with a tape measure in front of my face, my pupils are 2 and 5/16″ apart, or 2.3 inches. The distance between the place between my eyebrows and my outstretched thumb is 23.5 inches. That’s a factor of 10.2, impressively close to the 10 I was promised.

Conclusion: This trick won’t give you an accurate distance, but as an estimation tool, it kind of works! And by the way, if you ever need to estimate how far away a deer statue is: a deer’s body length is about 5 feet.


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