Common grades and what they are used for
The conversions below are exact trigonometric equivalents; the usage notes cite the issuing standards and common site-work conventions.
| Grade | Angle | Ratio | Typical context |
|---|---|---|---|
| 2% | 1.15° | 1:50 | Common minimum surface slope for drainage away from buildings and across pavements |
| 5% | 2.86° | 1:20 | Maximum running slope for accessible walking surfaces before they count as ramps (ADA) |
| 6.67% | 3.81° | 1:15 | Worked-example slope; gentle embankment or driveway |
| 8.33% | 4.76° | 1:12 | Maximum running slope for new accessible ramps (ADA) |
| 10–12% | 5.7–6.8° | 1:10–1:8.3 | Steep driveway territory; many local codes cap driveway grades in this region |
| 100% | 45° | 1:1 | A 45° slope — rise equals run |
- A 100% grade is a 45° angle, not a vertical face — percent grade and degrees are different scales that only coincide near zero.
- Requirements differ by jurisdiction and use: the ADA Standards govern accessible routes in the US, road authorities set maximum street and driveway grades locally, and drainage minimums come from building codes and site-design practice. Verify the governing standard for your specific application.
What is elevation grade?
Elevation grade (or gradient) expresses how steeply the ground rises or falls, as the ratio of vertical rise to horizontal run. A 10% grade rises 10 units for every 100 units of horizontal distance. The same slope can be written three ways: as a percentage (rise ÷ run × 100), as an angle in degrees (the arctangent of rise ÷ run), and as a ratio of 1 vertical unit to n horizontal units (1:n, common in accessibility and drainage specifications).
Different trades favor different conventions. Roads and site work are usually specified in percent, accessibility standards use ratios (the ADA limits new ramp runs to 1:12), and equipment and roof work often quote degrees. Because all three describe the same rise/run triangle, this calculator reports them together, along with the slope length — the actual distance along the incline, which is what materials laid on the slope (pipe, turf, handrail) must cover.
How to use this elevation grade calculator
- Measure the vertical rise between the two points (with a level and grade rod, a laser level, or from spot elevations on a plan) and enter it.
- Measure the horizontal run between the same two points — the flat map distance, not the distance along the ground — and enter it in the same unit.
- Read the grade in percent, the angle in degrees and the 1:n ratio.
- Use the slope length when ordering materials that run along the incline, such as pipe, edging or handrail.
The formula behind elevation grade
Grade percentage equals rise divided by run, multiplied by 100. The angle in degrees is the arctangent of rise ÷ run. The ratio expresses the same relationship as 1 vertical to (run ÷ rise) horizontal, and the slope length is the Pythagorean hypotenuse √(rise² + run²).
Worked example: a 2 m rise over a 30 m run gives a grade of (2 ÷ 30) × 100 = 6.67%, an angle of arctan(2/30) ≈ 3.81°, and a ratio of 1:15. The slope length is √(2² + 30²) ≈ 30.07 m — barely longer than the run at this gentle grade, but the difference grows quickly on steep slopes.
Common mistakes
- Measuring the run along the sloping ground instead of horizontally — the run in every slope formula is the flat, map-distance component, and using the surface distance understates the true grade.
- Confusing percent with degrees — a 10% grade is about 5.7°, not 10°; the two scales diverge as slopes steepen.
- Mixing units between rise and run (e.g., rise in centimeters, run in meters), which scales the grade by the unit ratio.
- Applying the ADA 1:12 ramp maximum to the sloped surface length rather than the horizontal run — the ratio is defined against horizontal projection.
अक्सर पूछे जाने वाले सवाल
How do I calculate percent grade?
Divide the vertical rise by the horizontal run and multiply by 100. A 2 m rise over a 30 m run is (2 ÷ 30) × 100 = 6.67% grade.
What is a 1:12 slope in percent and degrees?
A 1:12 slope rises 1 unit for every 12 horizontal units, which equals 8.33% or about 4.76°. It is the maximum running slope the ADA Standards permit for new accessible ramp runs.
Is a 10% grade steep?
For roads, yes by most standards — many highway design guides keep grades well below 10%, and local codes often cap driveways around 10–12%. As an angle it is only about 5.7°, which illustrates how percent grade and degrees are different scales.
What grade do I need for drainage?
A commonly used minimum for shedding water across paved surfaces and graded ground near buildings is about 2% (1:50). Building codes additionally specify how ground must fall away from foundations; the governing code for the site applies.
What does a 100% grade mean?
A 100% grade means the rise equals the run, which is a 45° slope. Percent grade can exceed 100% on very steep terrain — a 200% grade is about 63.4°.
संदर्भ
- US Department of Justice — 2010 ADA Standards for Accessible Design: 1:12 maximum running slope for new ramp runs; 1:20 threshold above which a walking surface is treated as a ramp.
- AASHTO — A Policy on Geometric Design of Highways and Streets (the Green Book): maximum grade guidance for roads by class and terrain.
- International Code Council (ICC) — International Residential Code (IRC): site grading and foundation drainage slope provisions.