How to Estimate Distances Quickly and Easily | The Old Farmer's Almanac

# How to Estimate Distances

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## Learn how to estimate distance quickly and easily

Body

Did you know that your arm is about ten times longer than the distance between your eyes? That fact, together with a bit of math, can be used to estimate distances between you and any object of approximately known size.

### How to Estimate Distances

Imagine, for example, that you’re standing on the side of a hill, trying to decide how far it is to the top of a low hill on the other side of the valley. Just below the hilltop is a barn, which you feel reasonably sure is about 100 feet wide on the side facing you.

• Hold one arm straight out in front of you, elbow straight, thumb pointing up.

• Close one eye, and align one edge of your thumb with one edge of the barn.
• Without moving your head or arm, switch eyes, now sighting with the eye that was closed and closing the other.
• Your thumb will appear to jump sideways as a result of the change in perspective.

How far did it move? (Be sure to sight the same edge of your thumb when you switch eyes.)

• Let’s say it jumped about five times the width of the barn, or about 500 feet.
• Now multiply that figure by the handy constant 10 (the ratio of the length of your arm to the distance between your eyes).
• Now you get the distance between you and the barn—5,000 feet, or about one mile. The accompanying diagram should make the whole process clear.

### Why Should You Have This Skill?

With a little practice, you’ll find that you can perform a quick thumb-jump estimate in just a few seconds, and the result will usually be more accurate than an out-and-out guess.

At a minimum, it will provide some assurance that the figure is in the ballpark—which, in many cases, is as close as you need to get.

This is a very handy trick if you’re hiking or out in nature, or even a photographer.

Just knowing that the length of your arm is about ten times the distance between your eyes helps you measure the distance between yourself and anywhere!