Elevation Grade Calculator

Frequently Asked Questions

How do I calculate grade percentage?

Grade% = (rise / run) x 100. A 1 ft rise over 20 ft of run = 1/20 x 100 = 5% grade.

What is a 10% grade in degrees?

arctan(0.10) = 5.71 degrees. A 10% grade rises 10 units for every 100 units of horizontal distance.

What is the maximum grade for a residential driveway?

Most codes allow 12-15% maximum. Some jurisdictions permit up to 20% for short sections. Check your local building code.

What grade is needed for drainage?

Minimum 2% grade (1/4 inch per foot) is required away from foundations per most building codes to prevent water infiltration.

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How This Calculator Works

Grade percentage is the ratio of vertical rise to horizontal run expressed as a percentage: grade% = (rise / run) x 100. The grade ratio (X:1) tells you how many horizontal units correspond to 1 unit of rise. The angle in degrees uses the arctangent function: angle = atan(rise/run) x (180/pi).

The reverse calculation: given grade% and run, rise = run x (grade/100).

Grade Classifications

Common grade categories by use:

Flat: 0-2% - drainage may be insufficient, ponding risk

Gentle: 2-5% - ideal for driveways, ADA ramps, pedestrian paths

Moderate: 5-10% - typical for residential streets, parking lots

Steep: 10-15% - challenging for vehicles in wet or icy conditions

Very steep: over 15% - difficult for most vehicles, usually requires special paving

ADA requirements for accessible routes: maximum 1:20 (5%) running slope, 1:48 (2%) cross slope.

Common Applications

Grade calculations appear in many construction and landscaping contexts:

Driveways: most building codes limit residential driveways to 15-20% maximum

Site drainage: minimum 2% grade away from foundations is required by most codes

ADA ramps: maximum 8.33% (1:12) slope for wheelchair accessibility

Stormwater: swales and channels need at least 0.5-1% to prevent standing water

Road design: local street grades typically 0.5-8%, maximum 12-15%

Pipe drainage: gravity sewer mains typically 0.5-2%

FAQ

What is a 5% grade in inches per foot?

5% grade = 5 inches of rise per 100 inches of run = 0.6 inches per foot. Over a 20 ft run, the total rise would be 20 x 0.05 = 1 ft.

What is the maximum driveway grade?

Most residential building codes allow 12-15% maximum. Some jurisdictions allow up to 20% for short sections. Check local codes. At 15% grade, a 20 ft long driveway rises 3 ft vertically.

What is the ADA maximum ramp slope?

1:12 (one inch of rise per 12 inches of run) = 8.33% grade. A 1-foot rise requires at least 12 feet of ramp length. Landings are required at the top, bottom, and at any turn.

How do I convert grade percent to degrees?

Angle = arctan(grade/100). A 10% grade = arctan(0.10) = 5.71 degrees. A 100% grade (1:1) = 45 degrees.

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