Map Scale
The map scale is printed in the map legend. It is given as a ratio of inches on the map corresponding to inches, feet, or miles on the ground. For example, a map scale indicating a ratio of 1:24,000 (in/in), means that for every 1 inch on the map, 24,000 inches have been covered on the ground. Ground distances on maps are usually given in feet or miles.
Map Scale Conversion Factors
Scale 
Representative Fraction
 Map in/mi 
Map in/ch 
map ft/in 
1:253,440 
253.44 
0.25 
0.0031 
21,120 
1:126,720 
126.72 
0.50 
0.0063 
10,560 
1:63,360 
63.36 
1.00 
0.0125 
5,280 
1:62,500 
62.50 
1.01 
0.0127 
5,208 
1:31,680 
31.68 
2 
0.025 
2,640 
1:24,000 
24.00 
2.64 
0.033 
2,000 
1:21,120 
21.12 
3 
0.038 
1,760 
1:15,840 
15.84 
4 
0.05 
1,320 
1:7,920 
7.92 
8 
0.1 
660 
Table 5.1. Map Scale Conversion Factors
Example 1  Convert the map scale of 1:24,000 (in/in) to (in/ft).
Step 1. Set up the cancellation table so all units will cancel, except the desired unit, ft/in.
On the map 1 inch is equal to 2,000 feet on the ground, 1:2,000 (in/ft).
Example 2  Convert the 1:2,000 (in/ft) to (in/mile).
Step 1. Set up the cancellation table so all units will cancel, except the desired unit, miles/inch.
On the map 1 inch is equal to 0.4 miles.
Example 3a  The map distance between two points is 6 inches. The map scale is 1:24,000 (in/in). What is the ground distance in feet?
Set up the cancellation table so all units will cancel, except the desired unit, feet.
The ground distance is 12,000 feet.
Using the Modified Acreage Grid (Transparency)
To use the acreage grid transparency, follow these steps:<
 Place the acreage grid transparency over the area to be measured.
 Count dots inside the sketched area. Count every other dot when dots fall on the boundary line.
 Multiply the total number of dots by the conversion factor on the map scale to determine the total acreage. (See Table 5.2.)
Map Scales and Equivalents
Scale 
Inches per mile 
Acres per square inch 
Conversion factor that each dot equals 
1:20,000 
3.168 
63.769 
1.736 Acres 
1:24,000 
2.640 
91.827 
2.500 Acres 
1:62,500 
1.014 
622.449 
16.946 Acres 
1:63,360 
1.000 
640.000 
17.424 Acres 
Table 5.2 Acreage Grid Overlay, Map Scales, and Equivalents.
Example 3b  Using the information in Example 3a, find the ground distance in chains, miles, and inches.
Step 1. Set up the cancellation table so all units will cancel, except the desired unit, chains.
12,000 feet = 182 chains
Step 2. Set up the cancellation table so all units will cancel, except the desired unit, miles.
Step 3. Set up the cancellation table so all units will cancel, except the desired unit, inches.
12,000 feet = 182 chains = 2.3 miles = 144,000 inches
Occasionally, a map may not provide a scale. The scale can be calculated by knowing the distance between two points on the map, and measuring the distance on the map. Also, if a map has section lines, the distance between section lines is typically 1 mile.
Example 4  The distance between point A and B is 6 inches on the map. The known ground distance is 3,600 feet. What is the scale in units of inches/foot?
The map scale is 1:600 inches/foot.
Example 5  Use the map scale in example 6. The known ground distance between points B and C is 1/2 mile. How many inches is does this distance correspond to on the map?
map scale = known distance / measured distance
Rearrange terms by multiplying each side by the measured distance and dividing each side by the map scale.
measured distance = known distance / map scale Step 1. Set up the cancellation table so all units will cancel, except the desired unit, feet.
Step 2. Use the map scale from Example 6 to find the map distance.
measured distance = known distance map scale measured distance = 2,640 feet 1 inch = 4.4 inches 600 feet
On the ground onehalf mile is the same as 4.4 inches on the map.
