How to Calculate Road Distance

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Modern mapping applications like Google Maps and Mapquest mean that, most of the time, we don't have to calculate road distance. We can just put in two locations and have the program automatically calculate the distance for us. Being able to calculate road distance with just a map and a few simple tools, however, is still a useful skill to have, especially in the middle of your trip, where you may not have Internet access. Also, new streets and roads in remote locations do not immediately make it onto map websites.

Things You'll Need

  • Map
  • Ruler
  • String
  • Paper
  • Pencil
  • Calculator

Look at the map scale. In the lower right- or left-hand corner, there will be a small graph that shows a unit that corresponds to distance on the map. For example, if the scale is 1 inch long and is labeled five miles, you know that 1 inch represents five miles. Hold a ruler next to it and measure it.

Source: http://www.lib.utexas.edu/maps/historical/dili_1943_scale.jpg
Source: http://www.lib.utexas.edu/maps/historical/dili_1943_scale.jpg

Lay one end of a string down on one end of the road on the map. Lay the string on top of the road so that it follows every curve as accurately as possible. If you don't have a string, tear a strip of paper off a sheet and bend it along the curves in the road instead.

Hold the string or paper so that you pinch it where the road starts and ends. Measure it with a ruler.

Multiply the length of the string by the scale. For example, if the string was 7 inches long and each inch represents 5 miles, the road is approximately 35 miles long.

Look for small sequential numbers next to the road on the map. These numbers indicate miles. On detailed maps, there may be a marker every mile, but on less-detailed maps it could be every 10 miles or some other scale.

Image courtesy of: http://www.kissimmeetouristinformationbureau.com/images/192-map.jpg
Image courtesy of: http://www.kissimmeetouristinformationbureau.com/images/192-map.jpg

Find the number at the beginning of the section of the road you're driving and the number at the end. If the numbers only show every several miles, estimate the location. For example, if the road ends between 50 and 60 miles, call it 55 miles.

Subtract the lower number from the higher to get the total distance. For example, if the road starts at the 25-mile marker and ends at the 55-mile marker, the total is 55 - 25 = 30 miles.

Tips & Warnings

  • The bigger the scale, the less detail the map will show for each road. This will make the roads seem shorter than they are, because switchback curves won't show up.

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