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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Accessible ramp planning starts with a small vertical measurement that can demand a surprisingly long route. The common 1:12 profile means 24 inches of rise needs 24 feet of horizontal run before landings, turns, handrails, edge protection, door clearance, and site approach are considered.

Slope ratio and grade describe the same steepness in different languages. A 1:12 ramp rises one unit for every 12 units of horizontal travel, which is about 8.33% grade. A larger second number, such as 1:16 or 1:20, is gentler but takes more space. That space often decides whether a ramp can run straight, turn at a landing, switch back, or needs a different site approach.

Horizontal run is not the diagonal ramp surface length. Accessibility slope is based on the level distance from the start of a ramp run to the end of that run. The sloped surface is slightly longer and matters for decking, surfacing, and handrail takeoff, but using it as the run makes a ramp look flatter than it really is.

Ramp planning terms and why they matter
Planning factor	What it controls	Common mistake
Rise	The vertical change from lower finished surface to upper finished surface.	Measuring rough framing instead of the finished walking surface.
Horizontal run	The distance used for the running slope ratio.	Using diagonal ramp length and making the slope appear gentler.
Landings	Flat areas for resting, turning, doors, and splitting long rises.	Counting only ramp run and missing the real route footprint.
Handrails and edges	Support, guidance, and protection from open sides or drop-offs.	Treating slope as the only accessibility requirement.

Landings make long climbs usable and give people room to stop, turn, open a door, or recover control. They also add real footprint. A ramp that needs 24 feet of run can need much more site length once top and bottom landings are included, and a 90 degree turn or switchback usually needs a larger clear landing than a straight run.

Handrails and edge protection enter the plan when the route has meaningful rise, open sides, or nearby drop-offs. They are not just accessories. Handrails affect clear width and extensions, while curbs, barriers, extended surfaces, or protected adjoining ground help keep wheelchair casters, walkers, and crutch tips on the ramp or landing surface.

Context changes the level of review. A small private residential threshold ramp may still need safe geometry, but public accommodations, commercial projects, multifamily work, schools, and funded projects can trigger ADA, building code, fire code, zoning, historic-property, or local accessibility requirements. Early slope math catches space problems, while final drawings still need the adopted rules for the site.

How to Use This Tool:

Measure the finished vertical rise first. Use the lower walking surface to the finished top landing or threshold, not rough framing height or an unfinished deck edge.

Choose Ramp preset for a door threshold, porch entry, deck switchback, garden path, or measured ramp starting point. Presets only seed the form; edit them to match the site.
Set Calculation mode. Use plan mode when the rise is known and the run needs sizing. Use check mode when you measured an existing horizontal run and want to know whether it is too steep.
Select Unit system, then enter Vertical rise. Keep the unit attached to the number, especially when switching between inches, feet, millimeters, centimeters, and meters.
Choose Slope profile. The 1:12 profile is the common maximum for new accessible ramp runs. Gentler profiles need more space but are usually easier to use.
In check mode, enter Measured horizontal run. Use the level floor projection from start to end, not the diagonal board or walking-surface length.
Enter Clear ramp width, Layout style, Handrail estimate, and Edge protection. These fields affect landing checks, material length, and review flags.
Open Advanced for landing length and width, cross slope, waste allowance, and side drop near an edge. These fields are useful when the site has a turn, switchback, open side, or nonstandard landing.
Review Slope Ledger, Landing Checks, Material Takeoff, Profile Compare, and Ramp Profile. Copy or download the tables when you need to share a first-pass plan.

If warnings appear, fix the geometry before using the material quantities. A ramp that passes slope but fails landing width, edge protection, or cross slope still needs design review.

Interpreting Results:

Slope Ledger shows the core geometry: rise, modeled run, actual or target ratio, grade percent, ramp surface length, run count, landings, and total path footprint. In plan mode, the modeled run is derived from rise and the selected profile. In check mode, the measured run is used to calculate the actual ratio and the extra run needed when the ramp is steeper than the target.

Landing Checks compares clear width, landing length, turn landing width, cross slope, handrails, edge protection, and nearby side drop against common ADA-style planning thresholds. A pass in this table means the entered value clears the modeled rule, not that every code condition for the site has been satisfied.

Ratio such as 1:12 means one unit of rise for every 12 units of horizontal run. Larger second numbers are gentler.
Grade converts the same slope into percent. A 1:12 ramp is about 8.33% grade.
Run count increases when the rise exceeds the selected per-run rise limit, commonly 30 inches for standard accessible ramp runs.
Path length with landings includes flat landing length, so it is closer to layout footprint than ramp run alone.
Material Takeoff estimates walking-surface area, landing surface area, handrail length, edge-protection length, and a surface material allowance with waste.
Profile Compare shows how the same rise changes under steeper or gentler profiles, which helps explain why a gentler ramp quickly needs more site length.

Technical Details:

Running slope is calculated from vertical rise and horizontal run. The calculator normalizes all length inputs to inches internally, applies the selected slope profile, then displays the results in the chosen unit system. The diagonal ramp surface length is calculated separately from horizontal run because material length follows the sloped surface while accessibility slope is based on horizontal travel.

Formula Core:

The same geometry works in imperial or metric units as long as rise and run use the same base unit.

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

Run segmentation uses the selected profile's maximum rise per run. A standard 1:12 accessible ramp run is commonly checked with a 30 inch maximum rise per run. Existing-site exception profiles are steeper and have much smaller modeled rise limits, so they should be used only when the exception is genuinely applicable.

Accessibility ramp planning thresholds
Planning check	Common threshold	How the calculator uses it
Running slope	1:12 maximum for standard ramp runs	Sizes target run or flags a measured run as too steep.
Maximum rise per run	30 inches for standard runs	Splits taller climbs into multiple runs with intermediate landings.
Clear width	36 inches minimum between leading handrail edges	Flags a ramp that is too narrow after handrails or edge details are considered.
Landing length	60 inches clear at top, bottom, and intermediate landings	Adds landing sections to the footprint and checks the entered clear length.
Turn landing	60 inches by 60 inches for direction changes	Applies the wider landing check for 90 degree turns and switchbacks.
Cross slope	1:48 maximum, about 2.08%	Flags side-to-side tilt that can make the route hard to control.
Handrails	Commonly required when ramp rise is greater than 6 inches	Includes or flags handrails based on the selected handrail mode.
Edge protection	Curb, barrier, extended surface, wall, or protected edge condition	Flags open-edge plans that need a curb, barrier, or other detailed protection.

The material takeoff is intentionally rough. It multiplies ramp surface length and landing area by clear width, then applies the selected waste allowance. It does not model posts, footings, framing spans, guard loading, fastening patterns, drainage, snow loads, or product-specific board spacing.

Limitations:

Accessibility rules are legal and design requirements, not just arithmetic. A correct slope number can still fail because of door maneuvering clearance, threshold details, landing slope, drainage, surface firmness, handrail shape, rail extension, guard requirements, curb transitions, lighting, turning space, or conflicts with stairs and exits.

Verify the adopted ADA standard, state accessibility code, local building code, and permitting requirements before construction.
Do not use existing-site exception profiles unless a qualified reviewer confirms that the project condition allows them.
Measure horizontal run, not diagonal ramp length, when checking an existing ramp.
Use finished surfaces for rise, width, landing, cross-slope, and side-drop measurements.
Have structural design, foundations, guards, handrails, drainage, and slip-resistant surfacing reviewed for the actual site.

Worked Examples:

Porch entry with 24 inches of rise:

A 24 inch rise at 1:12 needs 288 inches, or 24 feet, of horizontal run. Because the rise is below 30 inches, the calculator can model it as one ramp run with top and bottom landings. The total path footprint becomes longer than 24 feet once the landings are added.

Deck switchback with 36 inches of rise:

A 36 inch rise at 1:12 needs 36 feet of horizontal run, but a single standard run cannot cover all 36 inches of rise. The plan is split into more than one run, and the switchback layout applies the 60 inch by 60 inch turn-landing check.

Measured ramp that is too short:

If a ramp rises 24 inches over an 18 foot horizontal run, the actual ratio is 1:9. A 1:12 target for the same rise needs 24 feet, so the result reports the extra run needed and flags the measured ramp as steeper than the selected profile.

Gentler garden route:

An 18 inch rise at 1:20 needs 30 feet of horizontal run before landings. The route is much longer than a 1:12 ramp, but the gentler grade can be easier for manual wheelchair users, walkers, carts, and anyone climbing the route repeatedly.

FAQ:

Is 1:12 always enough for ADA compliance?

No. A 1:12 running slope is only one part of ramp design. Width, landings, cross slope, handrails, edge protection, surface, door clearance, and local code requirements still need review.

Why does the tool use horizontal run instead of ramp board length?

Accessibility slope is rise over horizontal travel distance. The diagonal surface length is useful for material takeoff, but it is not the value used to calculate the slope ratio.

What slope is easier than 1:12?

A larger ratio denominator is gentler. For example, 1:16 and 1:20 both need more run than 1:12 for the same rise, but the climb is less steep.

When are handrails included?

The automatic handrail mode includes handrails when rise is greater than 6 inches, a common ADA-style trigger. You can also force handrails on or omit them from the rough takeoff, but the final design still needs code review.

Can this estimate materials for construction?

It gives a first-pass walking-surface, landing, handrail, and edge-protection takeoff. Structural framing, foundations, guards, fastening, product waste, and site preparation must be estimated separately.

Glossary:

Rise: The vertical height from the lower finished surface to the upper finished landing or threshold.
Run: The horizontal travel distance of the ramp, excluding flat landings unless the result specifically says footprint.
Running slope: The direction-of-travel slope, commonly written as a ratio such as 1:12 or as a grade percent.
Cross slope: The side-to-side slope across the ramp or landing surface.
Landing: A level resting and turning area at the top, bottom, or between ramp runs.
Edge protection: A curb, barrier, extended surface, wall condition, or similar detail that helps keep wheels and mobility aids on the ramp or landing.

References:

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