A grading contractor must understand how slopes are described to avoid confusion or substantial errors in calculation. Slope is important in many real world situations. For example, a wheelchair ramp must be built so that its grade or steepness is small enough that people in wheelchairs are capable of going up the ramp on their own. In addition, roads along the hillsides are designed with an allowable grade so that vehicular traffic does not drive out of control.

Slopes may be described in two ways, in degrees of slope or as a percentage of slope. The diagram below illustrates how these two approaches are related:

1. Degree of slope = the angle between the slope and the horizontal.

2. Percentage of slope % = the units of vertical rise compared to the units of horizontal travel.

Note 1: The slope of a road is called its grade. A steeper road and has a higher grade and is more difficult to climb or slow down going downhill.

Note 2: The percentage of slope (%) is always a larger number than the equivalent degree of slope. Therefore, it’s essential to know which is being used.

100' Horizontal

Grading plans frequently refer to a 1H:1V or a 1-1/2H to 1V slope when indicating the steepness of a cut or fill slope. These terms mean one foot horizontal to one foot vertical or one and one half feet horizontal to one foot vertical. Relating these to percent, a 1H:1V slope = 100% slope = 45 degree angle and 1-½:1V slope = 66.7% slope = 33 degree angle.