How to Estimate Distance Using Only Your Thumb
One of the most frustrating hobbies I’ve ever had was archery, but not because it’s hard to hit the target on the wall (it is, but I was good at it). My problem was that one of the popular ways to have fun with archery was “3D Shooting” where you had to shoot a series of animal statues, each located at an unknown distance.
The estimate of the distance turned out to be my mistake. If you don’t have a clear idea of how far away the fake deer is, you will end up shooting it through the back or burying your arrow underground under its feet. At the time, I believed that estimating distance was not a skill that could be learned, but rather an intuition. Hence my surprise when I recently stumbled upon a quick math trick that allows anyone to estimate distance fairly accurately.
This method involves some assessment at the level of the gut, but a much simpler type. Then you just multiply by 10. Here’s how it works:
- Hold your thumb in front of you (with your arm fully extended) and close one eye. Hover your thumb over an object that you know the size of (such as a car).
- Without moving your thumb, close the open eye and open the other. Your thumb will be in a different place.
- Assess how far your thumb has “moved” relative to the object you’re looking at. For example, a car is about 15 feet long, so if your thumb moves half the length of the car, that’s about 7.5 feet.
- Multiply by 10. In this example, you would calculate that the car is about 75 feet away from you.
Too good to be true? I went and tried. I also took a laser rangefinder and a tape measure with me to check. One thing I immediately noticed was that I was tempted to measure the distance between the two images of the thumb; instead, you need to measure the distance from, say, the left side of the first thumb image to the left side of the second thumb image.
Standing in the kitchen, looking at the TV in the other room, I estimated that the TV was somewhere between 3 and 4 feet wide, and that my thumb had moved a little more than half its distance, about 2 feet. Calculation: TV should be 20 feet away. Laser level says: 25 feet. Okay, not bad.
From my desk to the nearest bookshelf, my thumb moved 6 inches, maybe a little more. Calculation: 60 inches. Actual size: 59 inches.
From a spot in my driveway to a garden shed: I turned my head sideways to measure the height of the door. Thumb distance should be about 6 feet (most of the height of the door), so the barn should be 60 feet apart. Actual size: about 70 feet. Not perfect, but again, close.
The reason this trick should work is because the distance from your eye to your thumb is about 10 times the distance from one eye to the other. I also measured this. Looking into a mirror with a measuring tape in front of my face, my pupils are 2 and 5/16 inches apart, or 2.3 inches. The distance from the point between my eyebrows to my outstretched thumb is 23.5 inches. This is a factor of 10.2. , impressively close to the 10 I was promised.
Bottom line: this trick won’t give you an accurate distance, but as a scoring tool it really works! And by the way, if you ever need to estimate how far away the statue in the form of a deer is: the body length of a deer is approximately 5 feet.