Slope / Grade Calculator: Calculate Rise, Run & Percentage (Free Tool)
You are building a ramp. You are laying a driveway. You are installing drainage. How steep should it be? Too steep, and it is unsafe. Too flat, and water does not drain.
Slope (grade) is the steepness of a surface. It is measured as rise over run, as a percentage, or as an angle.
Today, I give you a free Slope / Grade Calculator.
You enter the rise (vertical change) and run (horizontal distance). The calculator shows:
- Slope as a ratio (rise:run)
- Slope as a percentage (%)
- Slope as an angle (degrees)
- Grade as a decimal
Let me explain how to calculate slope and grade.
What is Slope? (Simple Explanation)
Slope is the steepness of a line or surface. It tells you how much a surface rises (or falls) over a given horizontal distance.
The formula:
Slope = Rise ÷ Run
Rise – Vertical change (how much it goes up)
Run – Horizontal distance (how far it goes)
Ways to express slope:
- Ratio – 1:12 (1 inch rise per 12 inches run)
- Percentage – 8.33% (rise ÷ run × 100)
- Angle – 4.76 degrees (angle of the slope)
- Grade – 0.0833 (decimal)
Why This Slope Calculator Matters
Here is why you need to calculate slope correctly.
Reason 1: ADA ramp requirements
ADA requires a maximum slope of 1:12 (8.33%) for wheelchair ramps. Calculate to ensure compliance.
Reason 2: Drainage and grading
Water needs slope to drain. Minimum slope for drainage is 1-2%. Calculate to prevent standing water.
Reason 3: Roof pitch
Roof pitch is measured as rise per 12 inches of run. A 6:12 roof rises 6 inches per 12 inches.
Reason 4: Driveways and sidewalks
Driveways need slope for drainage but should not be too steep for vehicles.
Reason 5: Road construction
Roads have maximum grade limits for safety and fuel efficiency.
The Slope Formula
Basic formula:
Slope Ratio = Rise ÷ Run
Slope percentage:
Grade % = (Rise ÷ Run) × 100
Slope angle (degrees):
Angle = arctan(Rise ÷ Run)
Grade (decimal):
Grade = Rise ÷ Run
LIVE Slope / Grade Calculator
Enter rise and run. The calculator shows slope in multiple formats instantly.
📐 Slope / Grade Calculator
📏 Rise (vertical change)
📏 Run (horizontal distance)
📐 Slope / Grade Calculator
Calculate rise over run, percentage, and angle
📏 Rise (vertical change)
Feet Inches
📏 Run (horizontal distance)
Feet Inches
📊 SLOPE (GRADE)
1 : 12.00
8.33 %
4.76°
0.0833
0%
💡 ADA ramp max slope: 1:12 (8.33%). Roof pitch: 6:12 is common.
📐 Rise ÷ Run = Grade. Grade × 100 = Percentage. arctan(Grade) = Angle in degrees.
How to Use This Slope Calculator
Follow these 4 simple steps.
Step 1: Enter the rise (vertical change)
Step 2: Select the unit (feet or inches)
Step 3: Enter the run (horizontal distance)
Step 4: Select the unit (feet or inches)
The calculator shows slope as a ratio, percentage, angle, and decimal.
Real Examples: Different Scenarios
Example 1: Wheelchair ramp (ADA)
- Rise: 12 inches (1 foot)
- Run: 12 feet
- Grade: 1 ÷ 12 = 0.0833 = 8.33% = 4.76°
Result: Meets ADA requirement (max 1:12)
Example 2: Roof pitch
- Rise: 6 inches per 12 inches run
- Run: 12 inches
- Grade: 6 ÷ 12 = 0.5 = 50% = 26.6°
Result: 6:12 pitch (standard for many homes)
Example 3: Driveway drainage
- Rise: 3 inches over 10 feet
- Run: 120 inches, Rise: 3 inches
- Grade: 3 ÷ 120 = 0.025 = 2.5% = 1.43°
Result: Good for drainage, gentle for vehicles
Example 4: Access ramp for a stage
- Rise: 24 inches (2 feet)
- Run: 24 feet
- Grade: 2 ÷ 24 = 0.0833 = 8.33%
Result: Exactly ADA maximum
Common Slope Standards
| Application | Max Grade | Ratio | Angle |
|---|---|---|---|
| ADA wheelchair ramp | 8.33% | 1:12 | 4.76° |
| Handicap parking | 2% | 1:50 | 1.15° |
| Driveway (residential) | 15% | 1:6.7 | 8.5° |
| Sidewalk | 5% | 1:20 | 2.86° |
| Roof (low pitch) | 14% | 1:7 | 8° |
| Roof (standard pitch) | 50% | 6:12 | 26.6° |
| Roof (steep pitch) | 100% | 12:12 | 45° |
| Road (highway) | 6% | 1:16.7 | 3.4° |
| Road (local street) | 10% | 1:10 | 5.7° |
| Drainage pipe | 1% | 1:100 | 0.57° |
Roof Pitch Chart
| Pitch (in/ft) | Ratio | Percentage | Angle |
|---|---|---|---|
| 1:12 | 1:12 | 8.33% | 4.76° |
| 2:12 | 1:6 | 16.7% | 9.46° |
| 3:12 | 1:4 | 25% | 14.0° |
| 4:12 | 1:3 | 33.3% | 18.4° |
| 5:12 | 1:2.4 | 41.7% | 22.6° |
| 6:12 | 1:2 | 50% | 26.6° |
| 7:12 | 1:1.71 | 58.3% | 30.3° |
| 8:12 | 1:1.5 | 66.7% | 33.7° |
| 9:12 | 1:1.33 | 75% | 36.9° |
| 10:12 | 1:1.2 | 83.3% | 39.8° |
| 11:12 | 1:1.09 | 91.7% | 42.5° |
| 12:12 | 1:1 | 100% | 45° |
ADA Ramp Requirements
| Requirement | Value |
|---|---|
| Maximum slope | 1:12 (8.33%) |
| Maximum rise per run | 30 inches (2.5 ft) |
| Minimum width | 36 inches |
| Landings | Every 30 inches rise |
| Landing length | 60 inches minimum |
| Cross slope | 1:48 (2%) maximum |
Drainage Slope Requirements
| Application | Minimum Slope |
|---|---|
| Gutters | 1/16″ per foot (0.5%) |
| Downspouts | 1/8″ per foot (1%) |
| French drain | 1% |
| Sewer pipe | 1-2% |
| Storm drain | 1-2% |
| Parking lot | 1-2% |
| Swale | 2-5% |
Calculating Cut and Fill
For construction projects, you need to calculate cut (removing earth) and fill (adding earth).
Volume = Area × Average Depth
Cut and fill slope: The slope of the excavation is measured as horizontal to vertical (e.g., 1:1 or 1:2). A 1:1 slope means 1 foot horizontal for every 1 foot vertical.
Frequently Asked Questions (FAQs)
1. How do you calculate slope percentage?
Slope % = (Rise ÷ Run) × 100. A 1-foot rise over 10-foot run = 10%.
2. What is a 1:12 slope?
Rises 1 unit for every 12 units horizontally. 1 inch rise per foot run = 8.33%.
3. How do you convert slope percentage to degrees?
Angle = arctan(Percentage ÷ 100). 8.33% = arctan(0.0833) = 4.76°.
4. What is the steepest slope for a driveway?
12-15% maximum for passenger cars. 8% recommended.
5. What is the slope of a 6:12 roof?
50% grade. 6 inches rise per foot run.
6. How do you calculate ramp slope?
Rise ÷ Run. For a 30″ rise over 30 ft run: 30 ÷ 360 = 0.0833 = 8.33%.
7. What is a 2% slope?
2% means 2 feet rise per 100 feet run (or 2 inches per 100 inches). Rises 0.24 inches per foot.
8. How do you calculate cut and fill slope?
Slope ratio (horizontal:vertical). 1:1 means 1 ft horizontal per 1 ft vertical.
9. What is the minimum slope for drainage?
1% (1 foot per 100 feet) for most drainage applications.
10. How do you find the angle of a slope?
Angle = arctan(rise ÷ run). Use calculator or online tool.
Common Mistakes
Mistake #1: Mixing units
Rise and run must be in the same units. Convert inches to feet (÷12) or feet to inches (×12).
Mistake #2: Confusing rise with run
Rise is vertical. Run is horizontal. Reverse them and the slope is inverted.
Mistake #3: Not accounting for existing grade
When building a ramp, the existing ground slope affects the total rise.
Mistake #4: Exceeding ADA limits
ADA maximum slope is 1:12. Slopes steeper than 1:12 are not allowed for wheelchair ramps.
Mistake #5: Using wrong units for roof pitch
Roof pitch is inches per 12 inches run. 6:12, not 6:1.
Slope in Different Fields
Architecture:
- Roof pitch
- Site grading
- Stair rise/run
Civil engineering:
- Road grades
- Drainage slopes
- Cut and fill
Landscaping:
- Terrace slopes
- Retaining walls
- Swale design
Construction:
- Ramp construction
- Driveway grading
- Floor slopes
Final Thoughts
Slope calculation is essential for construction, accessibility, and drainage.
My Slope / Grade Calculator gives you:
- Ratio (rise:run)
- Percentage grade
- Angle in degrees
- Decimal grade
Bookmark this page. Use it for ramps, roofs, driveways, and drainage.
The next time you need to know how steep a slope is, you will have the answer.
Disclaimer: This is an educational tool. For critical construction, consult an engineer.
External Links (Authority Backlinks):
- Wikipedia – Grade (slope){:target=”_blank” rel=”noopener noreferrer”}
- Wikipedia – Roof pitch{:target=”_blank” rel=”noopener noreferrer”}
- Wikipedia – ADA compliance{:target=”_blank” rel=”noopener noreferrer”}
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