Wheelchair Ramp Slope Calculator
Compute the slope of a wheelchair ramp as a ratio, percentage, or angle — or find the run needed for a given rise. Checks compliance against the ADA 1:12 maximum (8.33 %) and the 1:20 preferred slope.
| Category | Ratio | Percentage | Angle | Status |
|---|
| Rise | Min run @ 1:12 | Ramp length (slope) | Landings required | Comments |
|---|
| Ratio | Percentage | Angle | Run per 1 m rise | Context |
|---|
Why 1:12
1:12 (8.33 %) is the maximum slope an unassisted wheelchair user can typically ascend without excessive effort. It also corresponds to roughly the upper bound of a self-propelled wheelchair's sustainable climbing capability over any useful distance. Steeper ramps force the user to rely on a helper or on powered mobility, defeating the purpose of an accessible route.
Landings and the 30 in rule
ADA requires a landing (level, at least 1.525 m long) at the top and bottom of every ramp and wherever the total rise exceeds 760 mm (30 in). A single unbroken run cannot exceed 9.14 m (30 ft). This limits the sustained physical effort a user must exert and provides a safe place to pause.
Cross slope and clear width
A ramp must be at least 915 mm (36 in) clear width and have a cross slope no steeper than 1:48 (2.08 %). Edge protection (a curb or rail) is required on any side where the drop exceeds 75 mm, and handrails are required on both sides for any rise over 152 mm (6 in).
When you can't meet 1:12
If the run available is too short, options include: lengthening the ramp with switchbacks and landings, using a platform lift or vertical platform lift, or (in existing facilities with documented infeasibility) invoking the ADA's "technically infeasible" exception. Never simply steepen the ramp and call it compliant — that is a common and expensive mistake.
How to Use This Calculator
The slope of a ramp is simply the ratio of vertical rise to horizontal run. Enter any two of the three values and the third appears instantly, along with a compliance check against the ADA and ISO 21542 thresholds.
1. Choose what to solve for
Most users know the rise (the step height) and want the run required to meet the ADA 1:12 rule — solve for Run. Or enter both to check whether an existing ramp is compliant — solve for Slope.
2. Enter the two known values
Type a number, drag the slider, or tap a preset. Each length field has its own unit selector (mm, cm, m, in, ft). The slope field switches between ratio, percentage, and angle.
3. Read the result card
The result appears large, with the ADA compliance category (preferred / compliant / non-compliant) shown below. All three slope notations are given in the metadata line.
4. Check the charts
The Slope triangle tab draws the ramp geometry with rise, run and angle annotated. Slope vs rise shows how the slope changes with rise at your fixed run. ADA compliance zones shows where your slope falls on a colour scale.
5. Reference tables
Table 1 lists the ADA slope categories. Table 2 gives the required run for common rises at 1:12. Table 3 (Advanced) converts between ratio, percentage, and angle.
6. Advanced mode
See sensitivity to each input, plus companion metrics: ramp surface length, landings required, cross-slope check, and the run you would need to reach the 1:20 preferred slope.
What This Tool Offers
A complete workbench for designing and checking wheelchair ramps against the ADA and ISO 21542 accessibility standards.
Three-way solve
Solve for slope, rise, or run from the other two values. Slope can be read as a ratio, a percentage, or an angle.
ADA compliance check
Instant category detection — preferred (≤ 1:20), compliant (1:12–1:20), or non-compliant (> 1:12) — with context.
Three interactive views
Slope triangle diagram, slope-vs-rise curve with the ADA boundary, and a colour-coded compliance zone bar.
Per-field unit switching
Rise and run switch independently between mm, cm, m, in, and ft. Slope switches between ratio, %, and degrees.
Reference tables
ADA slope categories, required run for common rises at 1:12, and slope unit conversions — all live-highlighted.
Companion quantities
Ramp surface length, landings required, cross-slope check, and the run needed to reach the 1:20 preferred slope.
What Is Ramp Slope?
Ramp slope is the ratio of vertical rise to horizontal run. It is expressed three ways in accessibility practice: as a ratio (1:12), as a percentage (8.33 %), or as an angle in degrees (4.76°). The ADA Standards for Accessible Design set 1:12 (8.33 %) as the maximum permitted slope for a newly constructed ramp in the United States, and 1:20 (5 %) as the preferred slope where space allows. ISO 21542 sets comparable limits internationally. Compliance is not just about the slope number — a compliant ramp also needs adequate landings, clear width, edge protection, and handrails, all of which are covered by the same standards.
Formula and Variables
Ramp length (hypotenuse) = √(Rise² + Run²)
| Symbol | Meaning | Notes |
|---|---|---|
| Rise | Vertical height overcome | m, mm, in, ft — the step or curb height |
| Run | Horizontal distance | m, mm, in, ft — the plan-view length of the ramp |
| Slope | Ratio of rise to run | Expressed as 1:X, %, or degrees |
| Ratio 1:X | 1 unit rise per X units run | ADA max X = 12; preferred X ≥ 20 |
| Percentage | (Rise/Run) × 100 | 1:12 = 8.33 % |
| Angle | arctan(Rise/Run) | 1:12 = 4.76° |
| Ramp length | √(Rise² + Run²) | The actual sloped surface — what you cut and install |
ADA / ISO 21542 Slope Categories
| Category | Ratio | Percentage | Angle |
|---|---|---|---|
| Preferred (walkway, no ramp required) | 1:20 or flatter | ≤ 5.00 % | ≤ 2.86° |
| ADA compliant maximum | 1:12 | 8.33 % | 4.76° |
| Existing facilities (limited exception) | 1:10 to 1:12 | 8.33–10.00 % | 4.76–5.71° |
| Non-compliant — steep | 1:8 to 1:10 | 10.00–12.50 % | 5.71–7.13° |
| Non-compliant — very steep | Steeper than 1:8 | > 12.50 % | > 7.13° |
Frequently Asked Questions
1:12 (8.33 %) is the steepest slope that an unassisted manual-wheelchair user can typically climb over a useful distance without an unreasonable physical demand. Steeper ramps force the user to rely on a helper or a powered wheelchair, which defeats the purpose of an independent accessible route. The Access Board's research in the 1980s and 1990s established this threshold, and it has been retained through every revision of the ADA Standards since.
1:20 (5 % or 1 unit rise per 20 units run) is the slope at which a surface is no longer considered a ramp at all — it is a walkway. No landings or handrails are required, and the surface can be walked or rolled with negligible effort. 1:12 (8.33 %) is the steepest permitted ramp slope, and requires landings, handrails, and edge protection. Where space allows, designers are encouraged to use the gentler 1:20 slope even when not strictly required.
The ADA requires a level landing at the top and bottom of every ramp, plus intermediate landings wherever the total rise exceeds 760 mm (30 in). A single unbroken run of ramp cannot exceed 9.14 m (30 ft). The rule of thumb is one landing for every 760 mm of rise — so a ramp with 1.5 m of total rise needs at least one intermediate landing, giving two runs of ≤ 760 mm rise each with a landing between them.
You cannot simply steepen the ramp — that makes it non-compliant. Options are: (1) lengthen the ramp with a switchback or L-shape using intermediate landings; (2) install a platform lift or vertical platform lift as an alternative to a ramp; (3) in existing facilities only, invoke the ADA's "technically infeasible" exception with documented justification; or (4) regrade the site so the change in level is smaller. In practice, the switchback layout is the most common solution for tight spaces.
Yes. The ADA requires a maximum cross slope of 1:48 (2.08 %) on any accessible surface, including ramps. Cross slope is what makes a wheelchair veer sideways and is a common cause of falls and fatigue. It is measured perpendicular to the direction of travel and is checked separately from the running slope. Construction tolerances typically allow a small exceedance but the design intent is that cross slope should be essentially flat.
What it means
The wheelchair ramp slope ratio, defined as Slope = Rise / Run, determines the incline of a ramp and is critical for safe and accessible mobility for individuals using wheelchairs, walkers, or other assistive devices. The Americans with Disabilities Act (ADA) mandates a maximum slope of 1:12 (1 inch rise per 12 inches run) for commercial and public facilities, which corresponds to approximately 4.8 degrees. This slope ensures that manual wheelchair users can ascend without excessive effort and can safely descend without losing control. The formula is used by architects, occupational therapists, and facility managers to design compliant ramps, with landings required at intervals (e.g., every 30 inches of rise) to allow rest and turning. For power wheelchairs, slightly steeper slopes may be tolerated, but 1:12 remains the standard. Understanding the slope ratio is essential for assessing existing ramps, planning modifications, and advocating for accessibility. It also applies to curb cuts, sidewalk ramps, and home entrances. Proper slope calculation prevents falls and overexertion, promoting independence and participation in daily activities.
Worked example
Wheelchair Ramp Slope – Two Examples
Real‑World| Parameter | Value |
|---|---|
| Rise | 4 in |
| Run | 48 in |
| Parameter | Value |
|---|---|
| Rise | 6 in |
| Run | 72 in |
Common mistakes
- Rise and run: Rise is vertical height, run is horizontal distance – both in the same units (e.g., inches, cm).
- ADA guideline: Maximum recommended slope is 1:12 (rise:run) – i.e., for every 1 unit of rise, at least 12 units of run. Steeper slopes may be allowable for short distances but require handrails.
- Ratio notation: A slope of 1:12 means for every 12 inches of horizontal run, the rise is 1 inch. Some express as a percentage (rise/run ×100).
- Landings: Ramps over 30 feet (9.1 m) require intermediate landings.
Applications
Wheelchair ramp slope ratio, defined as rise over run, is regulated by accessibility standards (e.g., ADA maximum slope 1:12) to ensure safe and independent access for people with mobility impairments. This slope calculation is used by architects, occupational therapists, and facility managers to design ramps that are not too steep for manual wheelchair use, while also accommodating space constraints. Correct slope design prevents excessive exertion, reduces the risk of falls, and complies with legal accessibility requirements. By using the slope ratio, professionals can create inclusive environments in public buildings, private homes, and community spaces, enhancing quality of life for individuals with disabilities.
- Design of accessible building entrances and pathways
- Modification of homes for wheelchair users
- Compliance with ADA and other accessibility standards
- Installation of temporary ramps for events and emergencies
- Assessment of existing ramps for safety and compliance
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