Calculate slope percentage, grade, and ratio from rise and run measurements. Essential for grading, drainage, and accessibility planning.
Slope percentage is the most common way to express grade in construction, landscaping, and civil engineering. It represents the vertical change (rise) relative to the horizontal distance (run), expressed as a percentage. A 2% slope means the ground drops 2 feet for every 100 feet of horizontal distance.
This calculator converts rise and run measurements into slope percentage, ratio, and angle. It's essential for grading plans, drainage design, accessibility ramps, road design, and landscape construction. Different applications have specific slope requirements — driveways (2‒12%), drainage swales (1–2%), and ADA ramps (max 8.33%).
Whether you're a contractor, engineer, or homeowner, understanding slope ensures proper drainage, safe walkways, and code-compliant construction.
Tracking this metric throughout the project lifecycle helps project managers identify potential issues early and maintain quality standards from foundation to final inspection. Integrating this calculation into the estimating workflow reduces reliance on rules of thumb and improves the accuracy of material takeoffs and budget projections for every job.
Slope is critical for drainage, accessibility, and structural applications. This calculator quickly converts between percentage, ratio, and angle formats, and checks your slope against common code requirements. Accurate figures enable contractors to prepare competitive bids with confidence, reducing the risk of underestimating costs or overcommitting on project timelines and deliverables.
Slope % = (Rise ÷ Run) × 100 Slope Ratio = 1 : (Run ÷ Rise) Angle = arctan(Rise ÷ Run) in degrees
Result: 3.0% slope (33.3:1 ratio, 1.72°)
Rise = 3 ft, Run = 100 ft. Slope = (3 ÷ 100) × 100 = 3.0%. Ratio = 100 ÷ 3 = 33.3:1. Angle = arctan(3/100) = 1.72°.
Drainage away from foundations: 5% for the first 10 ft (6 inches in 10 ft). Walkways: 2% max cross-slope (ADA). Ramps: 8.33% max (1:12). Driveways: 2‒15%. Parking lots: 1–5%. Swales: 1–2%. Roofs: 2‒25% depending on type.
Percentage: rise/run × 100 (most common in construction). Ratio: horizontal:vertical like 4:1 (used in earthwork). Angle: degrees from horizontal (used in engineering). Inches per foot: rise in inches per 1 foot of run (used for plumbing and roofing).
Proper slope prevents water damage to structures and landscapes. The building code typically requires 6 inches of fall in the first 10 feet from a foundation (5% slope). Beyond that, 1–2% slope is sufficient for sheet drainage.
If the existing grade slopes toward your house, you may need to re-grade, install a swale, or add a French drain. Measure the existing slope first, then design the correction. Sometimes just 1–2 inches of grade change over 10 feet solves the problem.
A 2% slope means the elevation changes 2 feet for every 100 feet of horizontal distance, or 1/4 inch per foot. This is the standard minimum slope for drainage — enough to move water without being noticeable to pedestrians.
Divide 100 by the slope percentage. A 2% slope = 100/2 = 50:1 ratio. A 4% slope = 100/4 = 25:1 ratio. A 33% slope = 100/33 = 3:1 ratio. Higher percentages mean steeper slopes.
Most riding mowers can handle up to 15% slope (about 7:1 ratio). Push mowers are safe up to about 25% (4:1). Slopes steeper than 33% (3:1) should be ground cover, retaining walls, or terraced. OSHA limits are 12% for equipment.
Outdoor concrete should slope at least 1% (1/8" per foot) for drainage, with 2% (1/4" per foot) preferred. Patios and pool decks often use 2%. Driveways can be steeper but should drain toward the street.
Place a long level (4+ ft) on the ground, level it, and measure the gap at the downhill end. Gap ÷ level length = slope. For longer distances, use a transit, laser level, or GPS survey equipment.
Most codes allow up to 12‒15% for residential driveways. In cold climates, 8‒10% is the practical limit due to ice. Above 10‒12%, heated driveway systems or special drainage may be required.