ADA Ramp Slope Calculator

How the math works

The ADA 2010 Standards for Accessible Design set a maximum running slope of 1:12 for ramps along an accessible route. That ratio drives every other number on the page: divide your vertical rise by the slope decimal (≈0.0833 for 1:12), and you have the minimum horizontal run.

Landings are the part most homeowner-grade calculators miss. ADA §405.7 requires a level landing at the top and bottom of every ramp — even a short one. The landing must be at least 60 inches long and at least as wide as the ramp it serves. Anytime the vertical rise exceeds 30 inches, you also need an intermediate landing to break the run.

For accessible routes, a 32-inch rise looks innocent until you do the math: 32 feet of ramp run, plus three 5-foot landings (top, bottom, and one intermediate). The total footprint is 47 feet of length — which usually forces a switchback configuration to fit in real space.

The formula

The calculator runs four steps in order, using constants straight from our ADA 2010 data table:

Minimum run (in) = rise (in) ÷ 0.0833
Intermediate landings = (rise ÷ 30, rounded up) − 1, never below zero
Total footprint (in) = run + (2 + intermediate landings) × 60
Handrails: required on both sides once rise exceeds 6 in

Two details are deliberate. We divide by the decimal 0.0833 rather than multiplying rise by 12, which makes the computed run a hair longer than the textbook answer — a design with zero slope margin fails the moment a form board settles. And the intermediate-landing count comes from §405.6's 30-inch maximum rise per ramp run: a 30-inch rise needs no mid-landing, but 31 inches needs one, because the rise must now be split across two runs.

Worked example: a 24-inch porch rise

A common conversion case: a storefront entry slab sits 24 inches above grade. Trace the numbers the way the calculator does:

• Minimum run: 24 ÷ 0.0833 = 288.1 in ≈ 24.0 ft of ramp at 1:12.
• Intermediate landings: 24 ÷ 30 rounds up to 1, minus 1 = 0 — the whole rise fits in one run.
• Landings: top plus bottom = 2 × 60 in = 120 in.
• Total footprint: 288.1 + 120 = 408.1 in ≈ 34.0 ft (about 10.4 m).
• Handrails: 24 in of rise is well past the 6-inch threshold, so they're required on both sides at 34–38 in, with 12-inch extensions.

That 34-foot straight shot is why real 24-inch installations are usually built as an L or a switchback: two 12-foot runs joined by a 60 × 60 inch turning landing (§405.7.4 requires the full 60-inch square wherever the ramp changes direction). Same compliance, half the linear yard space.

ADA vs. residential code: what actually differs

Private single-family homes are not covered by the ADA — the International Residential Code governs instead, and it is meaningfully looser. Public, commercial, and covered multifamily work follows ADA 2010 (the IBC's ramp provisions align with it). Side by side:

A private ramp built to ADA numbers always satisfies the IRC; the reverse is not true. If the property could ever host clients, tenants, or a home daycare, build to the ADA column.

Handrail and width rules in plain language

Handrails are required on both sides if the rise exceeds 6 inches (ADA §405.8). They live between 34 and 38 inches off the ramp surface, run continuously across landings, and extend 12 inches past the top and bottom of each ramp run.

Minimum ramp width is 36 inches between handrails — meaning the actual framed-out width is typically 42–48 inches to leave handrail clearance and graspability. Edge protection (a curb, wall, or railing) is required when the ramp drops off above grade, even if handrails are present.

Cross slope and surface

Maximum cross slope is 1:48 (about 2%) — easy to miss when pouring concrete on uneven ground. Surface must be stable, firm, and slip-resistant; loose gravel and unsealed wood plank fail inspection. ADA §302 covers surface requirements.

Common mistakes inspectors flag

• Missing top landing. Builders sometimes attach the ramp directly to a doorway with no landing — fails immediately.
• Wrong handrail height. Heights outside 34–38 inches are a non-compliance, including handrails sloped to match the ramp surface.
• Slope just over 1:12. Inspectors carry digital levels. A nominal 1:12 design often comes in at 1:11.5 after framing tolerance; design to 1:14 for margin.
• Cross slope from drainage crown. A ramp that drains correctly may exceed 1:48 cross slope; needs a small swale beside the ramp instead.
• Non-graspable handrails. A flat 2×6 on edge is not a compliant gripping surface — §505.7.1 requires a circular section 1.25–2 inches in diameter (or an equivalent-perimeter shape), and §505.10.1 requires the 12-inch horizontal extensions at both ends of every run.

When this calculator is the wrong tool

Use a different reference for: curb ramps at sidewalk-street transitions (ADA §406 — separate cross-slope and counter-slope rules), vehicle loading ramps for trucks, theater accessible seating routes, or ramps inside airplanes and rail cars (other federal codes apply). This calculator targets §405 ramps along an accessible route in or to a building.

Sources & how we keep this current

Every constant in this calculator lives in a versioned data file, and each result ships with its citations so you can hand the output to a plan reviewer:

• ADA 2010 Standards for Accessible Design (Department of Justice) — §405 for slope, rise limits, landings, width, and cross slope; §505 for handrail height, gripping surface, and extensions. Public domain, hosted at ada.gov.
• US Access Board technical guides — the interpretive layer inspectors lean on for edge cases like sloped handrail extensions and edge protection details.
• International Residential Code R311.8 — the residential ramp rules in the comparison table above, for single-family work outside ADA jurisdiction.
• Fair Housing Act design requirements (24 CFR §100.205) — the basis for the covered-multifamily use case, which mirrors ADA §405 dimensions.

The ADA dimensional requirements are stable — the 2010 Standards remain the enforceable federal baseline — so updates here are rare, but we re-verify the data file against ada.gov whenever the DOJ or Access Board publishes new guidance. State and local amendments can be stricter (California's CBC Chapter 11B, notably), so always confirm against the code your permitting authority has actually adopted.