Percent Slope Calculator
Percent slope is the steepness of a surface written as a percentage: rise divided by run, times 100. A driveway that climbs 10 feet over 100 feet of horizontal distance has a 10 percent slope. This calculator runs that math in both directions, from rise and run or from an angle in degrees, and returns the percent slope with the equivalent angle, the 1:N slope ratio, a plain-language steepness reading, and an ADA ramp check no rival tool performs.
Quick Answer
A driveway that rises 10 feet over a 100-foot horizontal run has a 10.00% slope. That is an angle of 5.71 degrees, a slope ratio of 1: 10.00 uphill, and a Moderate steepness reading: comfortable for a driveway, but it fails the ADA ramp check, which caps accessible ramps at 8.33%. The calculator above is pre-filled with this exact driveway, so click Calculate to see it run.
Key takeaways
- Percent slope = (rise / run) x 100. It is not the same number as the angle in degrees: a 10% slope is only a 5.71-degree incline.
- Rise and run must be measured in the same units. Ten feet of rise over 100 yards of run is 3.33%, not 10%, and mixed units are the most common source of wrong slope numbers on real job sites.
- The ADA ramp check runs only in the Rise and Run mode. The Degrees to Percent mode converts tan(angle) x 100 and reports the plain meaning, without the accessibility verdict.
- A negative rise produces a downhill reading with a negative percent, and the run is measured horizontally, never along the sloped surface.
- Quick Answer
- What a slope percentage is actually telling you
- How to run either mode of the calculator
- The two formulas behind the numbers
- Worked examples: a driveway, a roof, a ramp and a downhill run
- Where percent slope shows up in the real world
- What the other slope calculators get wrong or leave out
- The four mistakes that produce wrong slope numbers
- Frequently asked questions
- Add This Calculator to Your Website
- References
What a slope percentage is actually telling you
A slope percentage answers one question: for every 100 units you travel horizontally, how many units do you climb? A 10% slope climbs 10 units for every 100 units of run. A 100% slope climbs 100 units for every 100, which is a 45-degree angle, and anything above 100% is steeper than 45 degrees. This is the same number road engineers call “grade”: a highway sign reading “6% grade” and a “6% slope” on a grading plan describe exactly the same hill, and federal highway signage standards show hill grades as percentages on warning signs.
If your numbers come from elevations on a site plan rather than measured lengths, the grade calculator handles that elevation-based form of the same idea.
| Percent slope | Angle | Ratio 1:N | Steepness reading | Typical example |
|---|---|---|---|---|
| 1% | 0.57 deg | 1: 100.00 | Gentle | Wheelchair-friendly path |
| 2% | 1.15 deg | 1: 50.00 | Mild | Minimum fall for patios and slabs |
| 5% | 2.86 deg | 1: 20.00 | Mild | Easy walking grade |
| 8.33% | 4.76 deg | 1: 12.00 | Mild | ADA ramp maximum |
| 10% | 5.71 deg | 1: 10.00 | Moderate | Typical driveway |
| 15% | 8.53 deg | 1: 6.67 | Steep | Upper end of residential driveways |
| 30% | 16.70 deg | 1: 3.33 | Very steep | Engineered slopes, retaining walls |
| 50% | 26.57 deg | 1: 2.00 | Very steep | 6:12 roof pitch |
| 100% | 45.00 deg | 1: 1.00 | Very steep | 45-degree incline |
The one rule that trips people up: rise and run must be in the same units. Ten feet of rise over 100 feet of run is 10 percent. Ten feet of rise over 100 yards of run is not 10 percent, it is about 3.33 percent, because 100 yards is 300 feet. Mixed units are the most common source of wrong slope numbers on real job sites.
How to run either mode of the calculator
Pick the tab that matches what you measured: Rise and Run for lengths, Degrees to Percent for an angle read from a clinometer or a level app. Enter the numbers and click Calculate; the result stays hidden until you click, and Reset returns the worked-example values.
- Rise and Run: enter the vertical change and the horizontal distance in the same units, then click Calculate percent slope. You get the percent slope, the equivalent angle in degrees, the 1:N slope ratio with an uphill or downhill note, a plain-language steepness reading, and the ADA ramp check with a pass or fail verdict.
- Degrees to Percent: enter the angle from 0 up to (but not including) 90 degrees, then click Convert to percent. You get the percent slope and its plain meaning, the units of rise per 100 units of run.
- Read the verdict rows: the steepness row translates the bare number (Gentle, Mild, Moderate, Steep, Very steep), and the ADA row tells you whether the slope is within the 8.33% maximum for accessible ramps.
- Copy or share: the Copy my results and Share results buttons sit side by side under every result, and they carry the full reading including the steepness label and the ADA verdict.
The two formulas behind the numbers
From rise and run, percent slope = (rise / run) x 100. From an angle in degrees, percent slope = tan(angle) x 100. The angle behind a rise and run pair is arctan(rise / run), converted from radians to degrees, which is the inverse of the tangent relationship described in standard trigonometry references.
Percent slope from degrees = tan(Angle in degrees) × 100
Angle from rise and run = arctan(Rise / Run), in degrees
Slope ratio = 1: (Run / Rise), per one unit of rise
The math behind the percentage itself is the same part-to-whole conversion our fraction to percent calculator handles for other contexts, and the angle conversion rests on the tangent and arctangent being inverse functions, as set out in OpenStax Algebra and Trigonometry, Section 8.3 on inverse trigonometric functions.
Worked examples: a driveway, a roof, a ramp and a downhill run
Every number below is a verified run of the calculator above, using the pre-filled driveway as the reference case. Enter any row yourself and you will get the same figures.
| Run | Percent slope | Angle | Ratio | Steepness | ADA check |
|---|---|---|---|---|---|
| Driveway: rise 10, run 100 | 10.00% | 5.71 deg | 1: 10.00 (uphill) | Moderate | Fails |
| Roof pitch 6:12: rise 6, run 12 | 50.00% | 26.57 deg | 1: 2.00 (uphill) | Very steep | Fails |
| ADA-limit ramp: rise 1, run 12 | 8.33% | 4.76 deg | 1: 12.00 (uphill) | Mild | Passes |
| Downhill run: rise -10, run 100 | -10.00% | -5.71 deg | 1: 10.00 (downhill) | Moderate | Fails |
The Degrees to Percent mode handles the reverse direction. A 30-degree trail descent converts to 57.74%, which is 57.74 units of drop per 100 units of horizontal travel, firmly in very steep territory for an unpaved path. A 45-degree incline converts to exactly 100.00%, the one slope where rise equals run and the percent lands on a round 100.
Here is where the worked driveway sits against the benchmarks that matter:
Roofers who think in pitch ratios will feel at home with the lean-to roof slope calculator, which speaks the language of roof framing rather than percentages.
Where percent slope shows up in the real world
The same percentage governs wheelchair ramps, drainage falls, trail difficulty, highway grades and roof pitches. Only the acceptable range changes with the job.
Wheelchair ramps and the ADA 1:12 rule
The 2010 ADA Standards for Accessible Design cap ramp running slope at 1:12, which is 8.33%, and the calculator checks every Rise and Run result against that limit with a pass or fail verdict. That limit is a maximum, not a target: gentler is always better for accessibility. Treat the verdict as a quick screening aid, not a code-compliance certification, because real accessibility compliance also depends on landings, handrails, cross slope and other requirements beyond the running slope.
Drainage falls for slabs, patios and yards
Water needs fall to move, and the industry rule of thumb for exterior slabs is a minimum 2% slope, about a quarter inch of drop per foot, so ponding never gets a chance to start. For an actual concrete pour, the concrete slope calculator works in the inches-of-fall-over-feet-of-run language flatwork crews use on site.
Trails, roads and roofs
Trail builders work in percent grades constantly: the Forest Service notes trail grades range from about 1% for wheelchair access up to 50% or more for scramble routes, with most high-use trails built in the 5 to 12% range. On highways, grade warning signs show the percent directly, a “6% grade” sign means 6 units of drop per 100 of run. On roofs, a 6:12 pitch is a 50% slope, steep enough that the calculator labels it very steep.
What the other slope calculators get wrong or leave out
Most rival tools compute rise over run correctly and stop there. The two strongest rivals beat this page on input flexibility, while none of them runs an accessibility check, which is exactly the gap this calculator was built to fill.
- Pearson’s slope percentage calculator: the strongest rival, with four input modes (rise and run, percent grade, angle, and 1-in-N ratio), a right-triangle illustration, a steepness gauge and a step-by-step solution. It has no ADA ramp check and no plain-language steepness verdict on the result.
- OnlyCalculators’ slope percentage calculator: lets you enter any two of rise, run, percent or angle and solves the rest, adds the slope distance (hypotenuse) and a percent-vs-angle table. It has no accessibility check and its steepness bands carry no plain-language reading of what the slope is good for.
- AreaCalculators’ percent slope calculator: covers the same two directions as this page with a formula table and solved step examples, but the tool is thin: no angle, ratio or steepness labels on the result, and no ADA check.
- BraveCalculator’s average slope calculator: a bare rise-and-run to percent tool with a worked example. No degrees conversion, no angle, no ratio, no steepness reading.
- CalculatorsHub’s fall percentage calculator: framed for drainage with a mixed-unit conversion table, useful for piping and grading. No degrees mode and no in-tool ADA check.
- CalculatorUltra’s slope percentage pages: formula pages with worked arithmetic but thin interactive depth.
The winning moves in this tool: it is the only tool of the set with an ADA 1:12 pass/fail verdict wired into the result; every Rise and Run result also carries the equivalent angle, the 1:N ratio with an uphill/downhill note, and a plain-language steepness reading; both directions of the math live on one page with copy and share on every result; and the worked examples, including a downhill run and the exact ADA boundary case, are verified runs of the tool itself rather than hand-waved numbers.
The four mistakes that produce wrong slope numbers
Nearly every wrong slope number on a job site comes from one of these four errors, and three of them are measurement mistakes, not math mistakes.
- Mixing units. Ten feet of rise over 100 yards of run is 3.33%, not 10%. Convert everything to one unit before you divide.
- Measuring along the slope. The run is the horizontal distance, measured level. A tape laid on the surface of the hill measures the hypotenuse, which is always longer than the run and always understates the slope.
- Confusing percent with degrees. A 10% slope is a 5.71-degree incline, not a 10-degree one. Only at 100% (a 45-degree angle) do the two numbers line up in a memorable way, and percent climbs far faster than degrees beyond that.
- Expecting the ADA check in Degrees to Percent mode. The accessibility verdict runs only in the Rise and Run mode. If you converted from degrees and need the ramp check, enter the equivalent rise and run (for example, 100 units of rise per 100 of run for 45 degrees) in the first tab.
Frequently asked questions
It means 10 units of vertical rise for every 100 units of horizontal run, an angle of about 5.71 degrees, and a slope ratio of 1: 10.00 uphill. A 10% driveway feels like a noticeable but comfortable hill, while a 10% ramp is too steep for wheelchair accessibility, which caps ramps at 8.33%.
Use percent slope = tan(angle in degrees) x 100. For example, tan(30 degrees) is 0.5774, so a 30-degree slope is 57.74%. The Degrees to Percent mode above does this instantly for any angle from 0 up to (but not including) 90 degrees.
Exactly 45 degrees. At 100%, rise equals run, and arctan(1) is 45 degrees. Slopes above 100% are steeper than 45 degrees: a 200% slope is about 63.43 degrees.
The 2010 ADA Standards for Accessible Design cap ramp running slope at 1:12, which is 8.33%, in Section 405.2. That means 1 unit of rise for every 12 units of run, and it is a maximum, not a target: gentler is always better. The calculator checks every Rise and Run result against this limit, but the verdict is a screening aid, not a code-compliance certification, because landings, handrails and cross slope matter too.
Yes. A negative rise, meaning a downhill slope, produces a negative percent slope, which simply indicates a decline rather than an incline. Enter the rise as a negative number and the tool reports the downhill ratio, with the steepness judged by the magnitude. A run of zero is rejected, because the slope is undefined there.
Yes. Grade is the term road and railway engineers use for percent slope. A 6% grade on a highway warning sign and a 6% slope on a grading plan are the same measurement: 6 units of rise per 100 units of run.
Most residential driveways fall between 5 and 15%. Above about 15%, cars can scrape, ice becomes dangerous and drainage needs engineering. Above 20 to 25%, many local codes require special review. Check your local building code before finalizing a steep driveway design.
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References
- U.S. Department of Justice. 2010 ADA Standards for Accessible Design, Section 405.2 (ramp running slope capped at 1:12). Accessed October 23, 2026.
- Federal Highway Administration. Manual on Uniform Traffic Control Devices, 2009 Edition, Part 2C: Warning Signs and Object Markers (Hill-Related Signs). Accessed October 23, 2026.
- The Concrete Network. Concrete Slope for Exterior Slabs: How to Ensure Proper Drainage. Accessed October 23, 2026.
- USDA Forest Service. Trail Construction and Maintenance Notebook, 0023-2839-MTDC: trail grade ranges. Accessed October 23, 2026.
- OpenStax, Rice University. Algebra and Trigonometry 2e, Section 8.3: Inverse Trigonometric Functions. Accessed October 23, 2026.