How to Measure Distances on a Map

How-To Steps

Woman's hands measuring on navigational chart.
Southern Stock/ Digital Vision/ Getty Images

Maps are useful for more than just directions. They can also help you determine the distance between two (or more) places. The scales on a map can be of different types, ranging from words and ratios to pictorial scales. Decoding the scale is the key to determining your distance.

Here's a quick guide on how to measure distances on a map. All you'll need is a ruler, some scratch paper, and a pencil. 

How-To Steps

  1. Use a ruler to measure the distance between the two places. If the line that you're trying to measure is quite curved, use a string to determine the distance, and then measure the string.
  2. Find the scale for the map you're going to use. They are typically located in one of the corners of the map. It might be pictorial—a ruler bar scale, or a written scale—in words or numbers.
  3. If the scale is a verbal statement (i.e. "1 inch equals 1 mile"), determine the distance by simply measuring it with a ruler. For example, if the scale says 1 inch = 1 mile, then for every inch between the two points on the map, the real distance on the ground is that number in miles. If your measurement on the map is 3 5/8 inches, that would be 3.63 miles on the ground.
  4. If the scale is a representative fraction (and looks like 1/100,000), multiply the distance of the ruler by the denominator (100,000 in this case), which denotes distance in the ruler units. The units will be listed on the map, such as 1 inch or 1 centimeter. For example, if the map fraction is 1/100,000, the scale says inches, and your points are 6 inches apart, in real life they'll be 6x100,000 so 600,000 centimeters or 6 kilometers apart. 
  5. If the scale is a ratio (and looks like 1:100,000), you'll multiply the map units by the number following the colon. For example, if you see 1:63,360, that means 1 inch on the map represents 63,360 inches on the ground, which is 1 mile.
  6. With a graphic scale, you'll need to measure the graphic, for example, white and black bars, to determine how much ruler distance equates to distance in reality. You can either take your ruler measurement of the distance between your two points and place that on the scale to determine real distance, or you can use scratch paper and go from the scale to the map.
    To use paper, you'll place the edge of the sheet next to the scale and make marks where it shows distances, thus transferring the scale to the paper. Then label the marks as to what they mean, in real distance. Finally, you'll lay the paper on the map between your two points to determine the real-life distance between them.
  7. After you've found out your measurement and compared it with the scale, convert your units of measurement into the most convenient units for you (i.e., convert 63,360 inches to 1 mile or 600,000 cm to 6 km, and so on).

Look Out

Watch out for maps that have been reproduced and have had their scale changed. A graphic scale will change with the reduction or enlargement, but other scales become wrong. For example, if a map was shrunk down to 75 percent on a copier to make a handout and the scale says that 1 inch on the map is 1 mile, it's no longer true; only the original map printed at 100 percent is accurate for that scale.