How to Calculate Longitudinal Slope


Longitudinal slope is one way of terming grade or incline, as in the grade of a highway. Determining longitudinal slope has various applications in real life. The grade of things like highways or ramps for the disabled is important to make sure safety is maintained, because if they are very steep or have a high grade, they are more dangerous or even impossible to navigate. The grade of a residential road, from its center to the curb, is important in insuring proper drainage of rainwater.

  • Determine the "run" or the length of your slope. Keep in mind this measurement is equal to the distance a vehicle would travel from the start point to the top of the slope if the road were flat; it doesn't measure the actual length of a road.

  • Determine the "rise" or the elevation of your slope; the rise equals how much higher the vehicle will be after driving from the bottom to the top of the road.

  • Calculate the grade or longitudinal slope of the road by dividing the rise, or elevation value, by the run, or length value; for example, if a highway rises 100 feet and its length is 1000 feet, divide 100 feet by 1000 feet to get .1 as the result.

  • Express the grade as a percent. Take the result from the previous step and multiply it by 100; according to our example, .1 is multiplied by 100 and the resulting grade is 10 percent.

Tips & Warnings

  • There are also some online calculators for various aspects of slope and grade, such as CSG Network's Grade Percent Incline and Downgrade Calculator.

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  • Photo Credit Road image by Janne Kallio from
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