How to Determine the Grade of a Hill
The steepness of roads or paths is measured using "grades" expressed as a percentage. The steeper the hill, the higher the percentage. There are several ways you can determine grades along a route either in advance (using a topographical map) or while actually traveling (using a GPS unit or an inclinometer).
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Instructions
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Planning
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Determine the grade of a hill by using a simple mathematic formula: D / L X 100 = Grade. "D" is the difference in height or elevation from the top to the bottom of the hill; "L" is the length of the hill. For example, the calculations for a hill which goes up 70 feet in vertical distance in 1,000 feet of horizontal distance is 70 divided 1,000, multiplied by 100, which equals 7. Expressed as a percentage, it's a 7 percent grade.
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Check various maps of the route you are planning. Some maps list grades, though often just the steepest.
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Get a topographical map which includes the route you are planning to travel. Use the contour lines to determine the change in elevation and the map's scale to determine distance. Then use the above formula to determine the grade of each hill along the route.
While Traveling
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Look for road signs posted in areas with particularly steep grades. They usually post the grade to expect in the immediate route ahead, e.g., "8 percent grade, next 6 miles". That doesn't necessarily mean the entire 6 miles will be 8 percent; rather, one or more sections of the road will be 8 percent in the next 6 miles.
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Purchase an inclinometer if you frequently cycle in hilly areas and would like to know the grade of the hills you are riding. Several brands of these incline-measuring devices are designed for cyclists. They can be mounted on your bike to give an instant grade readout (see Resources below).
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Use a GPS unit to measure grades. All GPS units can determine elevation above sea level. Most will store that information as a waypoint in the unit's memory. Make a waypoint at the bottom of a hill, go to the top, and the GPS will determine the change in elevation and distance to the waypoint at the bottom. Use the figures and the above formula to calculate the grade of the hill.
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Tips & Warnings
When calculating grades mathematically, be sure you are using the same units of measure. Whether measuring in feet, meters, yards or miles, the grade, expressed as a percentage, will be the same.
