Rise Over Run To Percent Slope Calculator

Convert a rise-over-run slope into percent grade, then see the matching degrees, radians, and normalized 1:N ratio for drainage, ramps, roofs, and grading work.

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Rise-over-run to percent slope Convert a vertical rise and horizontal run into percent grade, then see the matching degrees, radians, and normalized 1:N slope.

Common presets

Horizontal run only

Percent slope uses rise divided by horizontal run, not the sloped surface length. Switching the measurement basis changes the result.

Percent can exceed 100%

Any slope steeper than 45° has a grade above 100% because the rise becomes larger than the horizontal run.

Enter rise and run Provide a rise and horizontal run to convert that slope into percent grade and related angle formats.

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Slope Helper

Rise-over-run to percent slope calculator: grade, degrees, and 1:N ratios explained

A rise-over-run to percent slope calculator turns a simple vertical-over-horizontal ratio into the percentage grade most people use in sitework, ramps, drainage, and grading notes. Enter the rise and horizontal run to see the percent slope first, then confirm the matching degrees, radians, and normalized 1:N ratio.

How rise-over-run becomes percent slope

Percent slope is the rise divided by the horizontal run, multiplied by 100. That is why a slope of 1 over 12 becomes about 8.33 percent grade and a slope of 1 over 50 becomes 2 percent.

The angle in degrees comes from the same triangle through the inverse tangent function. One geometry relationship therefore supports several ways to describe the same incline.

Percent slope = (rise / run) × 100

Reports grade as a percentage of the horizontal run.

Angle = arctan(rise / run)

Converts the same ratio into degrees or radians.

1:12 = 8.33% ≈ 4.76°

Common accessibility benchmark for relating ratio, percent, and angle.

Why horizontal run matters

Rise-over-run uses horizontal distance, not the sloped distance measured along the surface. If the wrong dimension is used in the denominator, the resulting percent grade will be understated.

That distinction matters in field checks, plans, accessibility discussions, and drainage notes. People may use the same words while measuring different lengths, which creates conflicting grade numbers.

Where percent slope is useful and where caution is needed

Percent grade is convenient when comparing drainage targets, site grades, roads, paths, and ramps because it is easy to read as change per 100 units of horizontal distance. It also lets you compare gentle and steep slopes on one consistent scale.

The result should still be treated as geometry, not a compliance ruling. Accessibility standards, design standards, and tolerances depend on the governing context and may define different limits for running slope, cross slope, and measurement conditions.

Further reading

Frequently asked questions

What is the difference between rise-over-run and percent slope?

Rise-over-run is the raw geometric ratio. Percent slope is that same ratio multiplied by 100, so a slope of 1 over 12 becomes about 8.33 percent.

 Can percent slope be more than 100 percent?

Yes. Any slope steeper than 45 degrees has a rise larger than the horizontal run, which makes the percent slope greater than 100 percent.

 Why does the calculator use horizontal run instead of slope length?

Because percent slope is defined from rise over horizontal run. Using the sloped surface length would understate the true grade.

 Does this calculator prove code or accessibility compliance?

No. It converts the entered geometry only. Compliance depends on the governing standard, field measurement method, tolerances, and project context.

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