Slope & Grade Calculator
Convert any way of expressing slope - rise over run, percent grade, or degrees - into all the others, plus the ratio form and the slope length. The fall table shows exactly how many inches of drop you need over common distances, which is the number you actually set your string line to. Formulas below.
Input
Results
Percent grade
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The formulas this calculator uses
Angle (°) = arctan(Rise ÷ Run)
Slope length = √(Rise² + Run²) · Fall = Distance × Grade ÷ 100
Recommended grades quick-reference
| Application | Grade | Fall per foot | Equivalent |
|---|---|---|---|
| Drain pipe (minimum) | 1% | 1/8 in | 0.57° |
| Patio / walkway drainage | 2% | 1/4 in | 1.15° |
| Yard grading at foundation (first 10 ft) | 5% | 5/8 in | 2.86° |
| ADA ramp maximum | 8.33% | 1 in | 4.76° (1:12) |
| Driveway comfortable max | 10% | 1-1/4 in | 5.71° |
| Driveway code max (typical) | 12–15% | 1.5–1.8 in | 6.8–8.5° |
| Mowable lawn slope max | 25–33% | 3–4 in | 14–18° (3:1 – 4:1) |
Common mistakes to avoid
Confusing percent with degrees. They are different scales: 100% = 45°. Contractors and plans use percent; only convert to degrees when an instrument requires it.
Measuring run along the slope. Run is the horizontal distance. On steep ground, taping along the surface inflates run and understates the true grade.
Grading toward the house. Even a slight negative grade at the foundation routes roof and surface water into the basement. Target 5% away for the first 10 feet.
When to call a professional
Site-wide regrading, slopes above 15%, retaining walls over 3–4 ft, or any slope showing cracks, slumpin
Assumptions used in this calculator
- Grade % = rise ÷ horizontal run × 100 (run measured level, not along the slope)
- Degrees = arctan(rise/run); 100% grade = 45°
- Fall table = distance × grade, expressed in inches
Change the adjustable inputs above where your project differs. Supplier figures and local codes govern; see our methodology.
Built for planning, not blind ordering. Verify dimensions, supplier conversions, local codes, and site conditions before construction.
Frequently Asked Questions
What does a 1% slope mean?
A 1% slope falls 1 foot over 100 feet, or about 1/8 inch per foot. It is the standard minimum for drainage pipes and hard surfaces that must shed water.
How do I convert percent grade to degrees?
Degrees = arctan(grade / 100). A 100% grade equals 45 degrees, not 90. For small slopes the numbers are close (1% is about 0.57 degrees), but they diverge as slopes steepen.
What slope should a patio have away from a house?
1/4 inch per foot, which is a 2% grade. A 12-foot patio should sit 3 inches lower at its outer edge than at the house.
What is the maximum slope for a driveway?
Most U.S. jurisdictions cap residential driveways around 12-15% grade. Above about 10%, expect scraping on transitions and traction problems in ice or snow; many designers target 8% or less.
How much fall does a drain pipe need?
Standard practice for 4-inch drain pipe is 1/8 inch per foot minimum (about 1%), with 1/4 inch per foot (2%) preferred where elevation allows.