Accessibility Ramp Slope Calculator

Check the ramp plan

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Ramp preset:

Use a preset to seed realistic rise, width, layout, and slope assumptions, then edit the fields.

Calculation mode:

Plan mode sizes the run. Check mode compares a measured run against the selected profile.

Unit system:

Switch display defaults for dimensions, tables, chart axes, and exports.

Vertical rise: {{ formatLength(riseIn, 2) }}

Every extra inch of rise adds one foot of run at a 1:12 profile.

Slope profile:

Use 1:12 for a common ADA maximum; choose gentler profiles when space allows.

Custom slope denominator: 1:{{ customSlopeDenominator }}

Use 12 or larger for a non-steeper-than-1:12 planning target unless a local exception applies.

Measured horizontal run: {{ formatLength(measuredRunIn, 2) }}

Check mode calculates actual ratio, grade, and extra run needed if the ramp is too steep.

Clear ramp width:

Use the clear travel width after handrails, curbs, or edge guards are installed.

Layout style:

The path length stays the same; the landing width check changes for turning layouts.

Handrail estimate:

Handrails may still be required by adopted code or project conditions; this controls takeoff estimates and checks.

Edge protection:

Choose the planned curb, barrier, extended surface, or protected-edge condition for open ramp sides.

Landing clear length:

Top, bottom, and intermediate ramp landings use this clear length in the footprint estimate.

Landing clear width:

For 90 degree turns or switchbacks, use at least 60 inches unless the local rule says otherwise.

Cross slope: {{ formatPercent(cross_slope_percent, 2) }}

Use the measured side-to-side slope across the ramp run or landing.

Surface waste allowance: {{ formatPercent(surface_waste_percent, 0) }}

Material takeoff multiplies ramp and landing surface area by this allowance.

Side drop near edge:

Enter the vertical drop-off within about 10 inches of the ramp or landing edge.

Measurement	Value	Planning use	Copy
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Check	Status	Evidence	Copy
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Item	Quantity	Basis	Copy
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Profile	Footprint	Tradeoff	Copy
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One step at an entrance can turn into many feet of accessible route once the path must work for a wheelchair, walker, stroller, delivery cart, or person who needs a slower climb. The slope ratio is the number people notice first, but the usable route also depends on clear width, level landings, cross slope, edges, handrails, drainage, door maneuvering space, and the room available on the site.

Running slope compares vertical rise with horizontal run. A 1:12 ramp rises 1 unit for every 12 units of level travel, so a 24 inch porch rise needs 24 feet of horizontal ramp before the top and bottom landings are counted. Gentler profiles such as 1:16 or 1:20 reduce effort and improve control, while steeper existing-site profiles need careful exception review because a short ramp can become difficult or unsafe quickly.

Ramp diagram showing vertical rise, horizontal run, top and bottom landings, and turning clearance

Ramp layout starts with three distances that are easy to mix together. Rise is the vertical change between finished walking surfaces. Run is the level projection used for the slope ratio. Surface length is the diagonal walking surface, which affects boards, decking, rails, and finishes but does not decide whether the ramp is too steep.

Ramp planning terms and common mistakes
Term	Meaning in ramp planning	Common mistake to avoid
Rise	Vertical height from lower finished surface to upper finished surface.	Measuring rough framing or unfinished threshold height.
Run	Horizontal travel distance for a ramp run.	Using diagonal ramp surface length as if it were horizontal run.
Landing	Level area for stopping, turning, door use, and splitting long climbs.	Counting only the sloped run and underestimating site footprint.
Cross slope	Side-to-side tilt across the travel direction.	Passing the running slope while leaving a surface that pulls users sideways.

Landings are part of the accessible route, not leftover floor area. They give a person a level place to stop before a door, make a turn, rest after a climb, or recover from a small steering error. A taller rise often has to be split into two or more ramp runs because each run is limited by the amount of rise it can cover before another level surface is needed.

A ramp can pass the running-slope check and still fail in use. Cross slope can pull a chair sideways, clear width can shrink after handrails or curbs are installed, an open edge can leave wheels unprotected, and water can drain across the travel path. Construction tolerance also matters because a design drawn exactly at the maximum slope has little room for field error.

Slope math is an early planning check, not a permit or inspection result. The final route still has to fit the site, match the adopted accessibility and building rules, and account for thresholds, doors, guards, surface firmness, slip resistance, lighting, drainage, and local review.

How to Use This Tool:

Use finished-surface measurements whenever possible. The results are most useful when the rise, run, width, landing, cross-slope, and side-drop values describe the route after threshold work, surfacing, curbs, guards, and handrails have been accounted for.

Choose Ramp preset for a realistic starting point such as a threshold, porch entry, deck switchback, garden route, or measured ramp. Edit the seeded values instead of treating the preset as a standard detail.
Set Calculation mode. Use Plan new ramp from rise when the vertical rise is known and the run needs sizing. Use Check existing ramp run when you already measured the horizontal run.
Select Unit system, then enter Vertical rise. Keep the unit beside the value, especially when switching among inches, feet, millimeters, centimeters, and meters.
Choose Slope profile. Use the 1:12 profile for a common ADA-style maximum, gentler profiles when the site has room, and existing-site exception profiles only when that exception has been confirmed.
For check mode, enter Measured horizontal run. Measure the level floor projection from the start of the ramp run to the end, not the diagonal deck or board length.
Enter Clear ramp width, Layout style, Handrail estimate, and Edge protection. These choices affect landing checks, handrail length, edge-protection review, and the path footprint.
Open Advanced when the site has a turn, switchback, open edge, unusual landing, or material estimate need. Adjust Landing clear length, Landing clear width, Cross slope, Surface waste allowance, and Side drop near edge.
Read Slope Ledger first, then check Landing Checks, Material Takeoff, Profile Compare, and Ramp Profile. If the warning list says to check the ramp plan, fix the missing or out-of-range input before using the quantities.

For a first pass, focus on required run, ramp-run count, landing count, and every failed check. Passing slope alone is not enough when clear width, landing width, handrails, cross slope, or edge protection still needs work.

Interpreting Results:

Slope Ledger gives the core geometry: vertical rise, selected profile, required or measured run, ramp surface length, grade, angle, ramp runs, landings, path footprint, and extra run needed. In plan mode, the selected profile sizes the run from the rise. In check mode, the measured run controls the actual ratio and can reveal a ramp that is too steep for the target profile.

Landing Checks is the main stop-and-review table. Treat any Needs work or Review result as a design issue, not a minor note, because the entered geometry has failed one of the common ADA-style planning checks or needs confirmation at the site.

A larger ratio denominator means a gentler ramp. A 1:16 profile is longer and less steep than 1:12 for the same rise.
Grade and angle describe the same slope in percent and degrees. A 1:12 slope is about 8.33% grade.
Ramp runs increases when the rise exceeds the selected per-run limit, commonly 30 inches for a standard accessible ramp run.
Path length with landings is closer to site footprint than run alone because it adds top, bottom, and intermediate landings.
Material Takeoff is a rough walking-surface, rail, edge-protection, and waste estimate, not a structural design or shopping list.
Profile Compare helps explain space tradeoffs by showing the same rise at steeper and gentler profiles.

Technical Details:

Ramp slope is a right-triangle relationship between vertical rise and horizontal run. The same equation works in imperial and metric units after both measurements are converted to a common length unit. The diagonal walking surface is then calculated from that triangle, while flat landings are added separately to estimate footprint and materials.

Accessibility review adds rule checks around the geometry. A ramp run may need to stop at a landing before it climbs too high, a direction change may require a wider level area, and handrails or edge protection can change the clear travel width. Those constraints explain why a ramp with enough horizontal run can still need layout changes.

Formula Core:

The primary ramp quantities follow from rise, horizontal run, and the selected slope denominator.

\begin{array}{lcl} target run & = & rise \times slope denominator \\ slope ratio & = & 1 : \frac{run}{rise} \\ grade percent & = & \frac{rise}{run} \times 100 \\ angle & = & \tan^{- 1} (\frac{rise}{run}) \times \frac{180}{π} \\ surface length & = & \sqrt{{rise}^{2} + {run}^{2}} \end{array}

For a 24 inch rise at 1:12, the target run is 24 x 12 = 288 inches, or 24 feet. The grade is 24 / 288 x 100, which is 8.33%. If the same 24 inch rise is measured over an 18 foot run, the actual ratio is 1:9 and the plan needs 6 more feet of horizontal run to reach 1:12.

Ramp variables and units
Quantity	Source	How it affects results
Rise	`Vertical rise`	Sets the required run, run count, handrail trigger, and total elevation in the ramp profile.
Run	Calculated in plan mode or entered as `Measured horizontal run` in check mode	Controls actual ratio, grade, angle, extra run needed, and path footprint.
Slope denominator	`Slope profile` or custom 1:X value	Multiplies the rise to find target run. Larger values are gentler and longer.
Clear width	`Clear ramp width`	Feeds width checks and walking-surface area estimates.
Landing size	`Landing clear length` and `Landing clear width`	Adds footprint and determines whether straight, turn, or switchback layouts clear the modeled landing rule.

Run segmentation is based on maximum rise per ramp run. The standard 1:12 profile uses a 30 inch maximum rise per run, so a 36 inch rise is split into two runs with an intermediate landing. Existing-site exception profiles are modeled with much smaller rise limits because they are steeper and intended for limited conditions.

Accessibility ramp planning checks and threshold behavior
Check	Modeled threshold	Pass condition
Selected slope target	Selected 1:X profile	Actual denominator is greater than or equal to the selected denominator.
1:12 benchmark	8.33% grade, or 1:12	Actual denominator is greater than or equal to 12. Steeper values are flagged for exception review.
Rise per ramp run	30 inches for the standard profile, lower for modeled exception profiles	Segment rise is less than or equal to the selected profile's per-run rise limit.
Clear ramp width	36 inches	Entered clear width is greater than or equal to 36 inches.
Landing clear length	60 inches	Entered landing length is greater than or equal to 60 inches.
Turn or switchback landing width	At least the ramp width, or 60 inches for turning layouts	Entered landing width meets the required value for the selected layout.
Cross slope	1:48, about 2.08%	Entered cross slope is less than or equal to 2.08%.
Handrails	Rise greater than 6 inches	Handrails are included automatically or manually when the rise exceeds 6 inches.
Edge protection	Curb, barrier, 12 inch extended surface, wall, or protected edge condition	Open edges are detailed, and protected-edge choices do not conflict with the entered side drop.

Material estimates are deliberately broad. Walking-surface area combines ramp surface area and landing area, then applies the selected waste allowance. Handrail length includes both sides plus simple extensions, and edge-protection length follows ramp and landing edges when a modeled protection method is selected. Structural framing, foundations, guard loading, fastening, drainage, slip resistance, snow or water exposure, and product-specific waste remain outside the estimate.

Limitations:

Ramp planning depends on adopted standards, site conditions, and project type. Numeric checks are useful for early layout decisions, but they do not replace code review, permitting, inspection, or professional design when those are required.

Confirm the ADA standard, state accessibility code, local building code, fire and egress requirements, and any project funding rules before construction.
Use existing-site exception profiles only when a qualified reviewer confirms that the exception applies.
Check door maneuvering clearance, threshold height, surface firmness, drainage, slip resistance, guard requirements, lighting, and transitions separately.
Measure finished surfaces. Rough framing, temporary decking, or unfinished thresholds can change rise, cross slope, clear width, and side-drop values.
Treat material quantities as a starting estimate. They do not model posts, footings, joists, anchors, load paths, or product-specific installation rules.

Worked Examples:

Porch entry with 24 inches of rise:

With Calculation mode set to plan mode, a 24 inch Vertical rise and a 1:12 Slope profile produce 24 feet of required horizontal run. Slope Ledger reports one ramp run because the rise is within the 30 inch single-run limit, while Path length with landings is longer after the top and bottom landings are included.

Deck switchback with 36 inches of rise:

A 36 inch rise at 1:12 needs 36 feet of run, but the rise is above the 30 inch single-run limit. The result splits the route into two ramp runs, adds an intermediate landing, and uses the switchback Layout style to check a 60 inch turning landing.

Measured ramp that is too steep:

In check mode, a ramp with 24 inches of rise over an 18 foot Measured horizontal run returns an actual slope of 1:9. Extra run needed reports 6 feet for a 1:12 target, and Landing Checks flags the selected slope target because the measured run is too short.

Open edge with a side drop:

If Edge protection is left as Open edge not detailed and Side drop near edge is greater than 1/2 inch, the edge-protection checks call for review. Switching to a curb, barrier, extended surface, or a genuinely protected edge should match a real site detail, not just clear the warning.

FAQ:

Does a 1:12 result mean the ramp is ADA compliant?

No. A 1:12 running slope is only one requirement. Check Landing Checks for width, landings, cross slope, handrails, and edge protection, then verify the full site against the adopted rules.

Why is horizontal run different from ramp surface length?

Horizontal run is the level distance used for the slope ratio. Ramp surface length is the diagonal walking surface, so it is useful for material takeoff but not for deciding whether the ramp is too steep.

What should I do when check mode says extra run is needed?

Use the Extra run needed value as the minimum added horizontal run for the selected profile. Then review landings and layout because adding run can require another landing or a turn.

Why did the warning list ask me to check the ramp plan?

The warning list appears when required values are missing or outside supported bounds, such as zero rise, zero measured run in check mode, a slope denominator below 1, a profile steeper than 1:8, or nonpositive landing dimensions.

Can the material takeoff be used for buying materials?

Use it only as an early quantity estimate. Material Takeoff covers walking surface, landing area, rough handrail length, edge-protection length, and waste allowance, but it does not size structure, foundations, guards, hardware, or drainage.

Glossary:

Rise: The vertical height between the lower and upper finished walking surfaces.
Run: The horizontal travel distance used to calculate the ramp slope ratio.
Running slope: The slope in the direction of travel, usually written as a ratio such as 1:12 or as a grade percent.
Cross slope: The side-to-side tilt across a ramp run or landing.
Landing: A level area at the top, bottom, or between ramp runs for stopping, turning, and door use.
Edge protection: A curb, barrier, extended surface, wall, or protected ground condition that helps keep wheels and mobility aids on the route.

References:

Chapter 4: Ramps and Curb Ramps, U.S. Access Board.
2010 ADA Standards for Accessible Design, ADA.gov.
ADA Accessibility Standards, U.S. Access Board.