Slope Grade Percentage Calculator

Slope Grade Percentage Calculator

Slope grade is typically expressed as a percentage (rise over run) rather than degrees in most landscaping and drainage contexts - this calculator gives you both figures from a simple rise and run measurement.

Grade% = (Rise / Run) x 100
Angle = atan(Rise / Run)

Example

3 ft rise over a 50 ft run:

Grade = (3/50) x 100 = 6.0% (3.43┬░) - a gentle, walkable slope

Reading the Grade

Grade	Assessment
Under 2%	Very flat - may need positive drainage design
2-10%	Gentle slope - suitable for most lawn and planting areas
10-25%	Moderate slope - may need terracing or erosion control
Over 25%	Steep - retaining walls or terracing likely needed

The 2% Drainage Rule

A widely used landscaping guideline recommends at least a 2% grade sloping away from building foundations to ensure proper drainage - insufficient slope near a foundation is a common cause of water infiltration and basement moisture problems, making this one of the more consequential grading details in overall property drainage design.