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SITE GRADING SLOPE CALCULATOR
Site Grading Slope & Elevation Calculator
Calculate a site grade's rise, fall, percent slope, angle and horizontal-to-vertical ratio from surveyed or measured elevations.
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BEFORE YOU START
Grading and drainage plan guide →Get a more useful result
Enter two elevations from the same vertical datum and a horizontal plan distance. Results describe one line segment, not a finished drainage design.
- Check both spot elevations and their common elevation datum.
- Measure actual horizontal run between the two locations.
- Read signed slope and grade direction; compare only to verified design limits.
Example: From elevation 105.50 to 103.50 over 50 horizontal feet is a 4% fall toward the end point.
INTERACTIVE ANALYSIS
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HOW IT WORKS
Useful Answers Without Pretending Every Property Is the Same
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WHY THIS TOOL MATTERS
Grading Slope Requires Two Elevations and a Run
Slope is the difference in vertical elevation divided by the horizontal distance between the measured points. A reliable calculation starts with an upper and lower spot elevation, or two numbered grades, tied to the same vertical datum. The horizontal distance should be measured in plan, not along the inclined ground surface. This tool uses feet for elevation and feet for run.
Slope Percentage Formula
Signed slope percent equals (end elevation minus start elevation) divided by horizontal run, multiplied by 100. If the start is at 105.50 feet, the end is at 103.50 feet and horizontal run is 50 feet, the signed slope is minus four percent, meaning a four-percent fall in the direction from start to end. The absolute slope magnitude is four percent.
Rise, Fall and Drainage Direction
The tool shows both signed elevation change and the absolute rise or fall. A negative change means that the end point is lower than the start; a positive change means it is higher. Water does not necessarily follow a single two-point section when the surrounding site has multiple grades, obstacles or surface depressions. The result should not be taken as a full drainage-flow analysis.
SOURCE & CONFIDENCE LAYER
Strong Tools Explain What Is Known, What Is Estimated, and What Still Needs Verification.
Verified sourceOfficial local or state resource when available
Preliminary resultCalculated or rules-based planning guidance
User suppliedFacts you entered about the property or project
Needs verificationProperty-specific issue the tool should not guess
DETAILED GUIDANCE
Use the Result Correctly Before You Commit Time or Money
Understanding a Horizontal-to-Vertical Ratio
Civil drawings sometimes express slope as H:V, or units of horizontal run to one unit of vertical change. A two-foot fall over fifty horizontal feet is 25:1 H:V, equivalent to four percent grade. For a level section, a finite H:V ratio cannot be stated meaningfully, so the tool labels it as level. A 1:1 grade corresponds to a 100 percent slope, not a one-percent slope.
Slope Angle in Degrees
The slope angle is the arctangent of rise divided by horizontal run, converted from radians to degrees. It may be more convenient for comparing steepness, while grading plans and stormwater reviewers commonly use percentage or profile elevations. This calculator displays the absolute angle as a numerical cross-check.
Comparing Against a Supplied Maximum
For planning you can optionally enter a maximum slope percentage supplied by the applicable project criteria. The tool compares the magnitude of the calculated slope with that entered threshold. This is not a code lookup and the entered number is not independently verified. A calculated value below the threshold still does not prove that the surface is accessible, drainable, constructible or safe.
When a Grading Plan Is Needed
A permit grading plan can require existing and proposed spot elevations, contours, drainage arrows, swale and inlet details, cut-and-fill information, erosion control and runoff calculations. Design and requirements vary with lot slope, paving, building changes, stormwater rules and local jurisdiction. A two-point slope calculation cannot replace an engineered grading or drainage plan.
Verify Survey Datum and Distances
Both elevations should refer to the same benchmark or vertical datum. Do not mix assumed slab height with surveyed NAVD88 or another reference without proper conversion. If the horizontal run is inferred from a resized drawing, first verify the drawing scale. Very small runs can produce misleadingly high slopes, so use actual reliable measurements.
Use the Result on a Permit Plan
A slope calculation may be included in an engineering profile, driveway section, walkway review or site drainage analysis when it is based on defensible measurements. Check grade direction, transition elevations and adjacent points; coordinate professional review for code-sensitive access, foundations and drainage.
FREQUENTLY ASKED QUESTIONS
Site Grading Slope & Elevation Calculator FAQs
These answers explain how to interpret the tool and when local or professional verification still matters.
How do you calculate percent slope?
Subtract starting elevation from ending elevation, divide by horizontal run, and multiply by 100. Negative means falling toward the end point.
What is the slope for 2 feet of fall over 50 feet?
The magnitude is 4 percent, a 25:1 horizontal-to-vertical slope. Signed slope is minus 4 percent from the higher start to the lower end.
Does a 4 percent slope mean four degrees?
No. Four percent slope corresponds to approximately 2.29 degrees. Percent slope and angle are different measures.
Does the tool calculate an ADA-compliant route?
No. Applicable slope limits, cross slopes, landings, transitions and surface requirements must be verified for the relevant route and code.
What if the beginning and ending elevations are equal?
The result is a level zero-percent grade with no finite H:V ratio.
What if I have the sloped distance rather than horizontal run?
Convert it from measured geometry first. The slope percentage formula needs horizontal distance, not length measured along the incline.
Can I use the result instead of a civil drainage plan?
No. Local runoff, boundary conditions, soil, stormwater conveyance and proposed finished grading require site-specific civil analysis.