Ramp Calculator – Slope, Run & Ramp Length

This ramp calculator finds the run, ramp length and slope (ratio, percent and angle) for any rise — checked against the ADA 1:12 standard and common loading slopes.

Run = Rise × Ratio; Length Is the Hypotenuse

A ramp is a right triangle: rise (vertical), run (horizontal), and the sloped surface between them (Pythagoras — √(rise² + run²), only slightly longer than the run at gentle slopes: +0.35% at 1:12). The vertical sibling problem — steps instead of slopes — is our Stair Calculator. Part of our Construction Calculators collection.

Worked Example (Verified)

• 24″ rise at ADA 1:12 (defaults): run = 24 ft (288″), ramp surface 24.08 ft, slope 8.33%, angle 4.76° — a two-foot doorstep consumes a 24-foot run: accessibility geometry is humbling arithmetic
• Same rise at loading slope 1:6 → 12 ft run — fine for a mower trailer, illegal for a public accessible route; slope choice is a use decision before it’s a math one
• A 30″ porch at 1:12 needs 30 ft of run AND exceeds nothing (30″ is exactly the max rise per run) — at 36″ you’d owe a landing and a switchback, doubling the footprint’s complexity
• Driveway check: 18″ of rise across a 15-ft apron is 1:10 (10%) — comfortable for cars; across 6 ft it’s 1:4 (25%), the scraping-bumpers zone

Choosing a Slope Honestly

• Accessibility: 1:12 is the maximum, not the target — 1:16 to 1:20 is kinder and 1:20 may escape “ramp” classification (no handrails) under ADA.
• Wet/icy exposure argues gentler: friction margins vanish on steep wet surfaces regardless of code compliance.
• Vehicle ramps trade breakover angle against length: long low cars ground out at the crest of steep short ramps even when the slope itself is climbable.
• Landings consume plan length: add 5 ft each (top/bottom, more for switchbacks) to the run when laying out space.

Related Tools

• Stair Calculator — the stepped alternative
• Roof Pitch Calculator — slope in pitch language
• Construction Calculators — the full collection

Frequently Asked Questions

How long does a ramp need to be for a 24-inch rise?

At the ADA maximum slope of 1:12, the run is 24 inches × 12 = 24 feet, and the sloped surface measures 24.08 feet. Plus landings: 5-ft level areas at top and bottom (and handrails, since rise exceeds 6″). This calculator gives run, surface length, percent and angle for any rise and standard slope.

What is the ADA ramp slope?

Maximum 1:12 (8.33%, 4.76°) for new accessible ramps, with a maximum rise of 30″ per run, minimum 36″ clear width, level landings, and handrails on both sides when the rise exceeds 6″. Gentler slopes (1:16–1:20) are recommended where space allows, and existing buildings have narrow exceptions — verify against the current ADA Standards and local amendments.

What’s the difference between run and ramp length?

Run is the horizontal distance the ramp covers; length is the actual sloped surface (the hypotenuse). At gentle slopes they’re within a fraction of a percent (24 ft run → 24.08 ft surface at 1:12); you buy materials by length and lay out space by run.

How do I express slope as percent or angle?

Percent = rise ÷ run × 100 (1:12 = 8.33%). Angle = arctan(rise ÷ run) (1:12 = 4.76°). All three languages describe the same triangle — this calculator reports all of them to keep drawings, codes and material specs in sync.

Can I build a steeper ramp at home?

Sometimes legally (private residential work has different code paths), but physics collects regardless: steeper means harder pushing, trickier descents, and worse wet traction. The presets here span ADA to vehicle loading so the trade-off is explicit — choose for the actual user on the worst day, not the strongest user on the best day.

Is this ramp calculator free?

Yes — free, instant, no sign-up. Geometry help; compliance sign-off belongs to your inspector.