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Slope & Grade Calculators | Free Construction Calculators

Calculate slopes, grades, ramp dimensions, and drainage requirements

Slope Calculator

Convert between slope formats

Ramp Calculator

Calculate ADA compliant ramp dimensions

Drainage Slope Calculator

Calculate required drainage slopes

Pitch to Slope Converter

Convert roof pitch to slope percentage

About Slope and Grade

Slope and grade calculations are fundamental to construction, civil engineering, and accessibility design. Understanding how to measure, express, and convert between different slope formats ensures proper drainage, accessibility compliance, and safe construction practices.

Slope Format Definitions

Percentage: Rise divided by run, multiplied by 100 (5% = 5 ft rise per 100 ft run)
Degrees: Angle from horizontal using trigonometry
Ratio: Expressed as 1:X (1:20 = 1 ft rise per 20 ft run)
Pitch: Common in roofing, expressed as rise:run (6:12 = 6 inches per foot)

ADA Ramp Requirements

Maximum Slope: 1:12 (8.33%) for new construction
Maximum Rise: 30 inches per ramp run
Landings Required: Every 30 feet of ramp run
Landing Size: Minimum 5 ft x 5 ft (60 inches x 60 inches)
Width: Minimum 36 inches clear between handrails
Edge Protection: Required on both sides
Handrails: Required on both sides if rise exceeds 6 inches

Drainage Slope Requirements

2-3 inch pipe: Minimum 1/4 inch per foot (2.08%)
4 inch and larger: Minimum 1/8 inch per foot (1.04%)
Storm drains: Can use lesser slopes based on diameter
Self-cleaning velocity: 2 fps minimum for proper drainage
Maximum slope: Typically limited to prevent excessive velocity

Site Grading Guidelines

Away from buildings: Minimum 5% (6 inches drop in 10 feet)
Lawns and landscaping: 2-5% for proper drainage
Paved surfaces: 1-2% minimum for water runoff
Walkways: Maximum 5% for accessibility without being a ramp
Driveways: Maximum 15-20% depending on climate

Roof Pitch and Slope

Low slope (flat): 0-2:12 pitch, requires membrane roofing
Standard slope: 4:12 to 9:12 pitch, most common for shingles
Steep slope: 10:12 and greater, excellent water shedding
Walkability: 6:12 and less can be walked safely with proper equipment
Material selection: Pitch determines appropriate roofing materials

Common Conversion Examples

Percentage to Ratio

2% = 1:50 (1 ft per 50 ft)
5% = 1:20 (1 ft per 20 ft)
8.33% = 1:12 (ADA maximum)
10% = 1:10 (1 ft per 10 ft)

Pitch to Percentage

3:12 = 25% slope
4:12 = 33.3% slope
6:12 = 50% slope
12:12 = 100% slope

Safety Considerations

Slopes over 10% can be difficult for pedestrians and wheeled equipment
Ice and snow accumulation increases danger on slopes over 5%
Mowing equipment typically limited to slopes under 25-33%
Erosion control measures needed on slopes over 10%
Always consider local climate and soil conditions

Code Compliance

Slope requirements vary by jurisdiction and application. Always verify calculations with local building codes, ADA standards, and site-specific conditions. For critical applications, consult with a licensed civil engineer or architect.