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* ADA recommends 1 inch rise per 12 inches length (1:12). Always verify local codes.
Every mobility ramp must balance safety, effort, and usable space. The gold standard – and the most common recommendation – is the ADA (Americans with Disabilities Act) 1:12 slope ratio. That means for every 1 inch (or 1 cm) of vertical rise, you need at least 12 inches (or 12 cm) of horizontal ramp length. So if your porch or threshold is 30 cm above ground, you need a ramp at least 360 cm long. That's exactly what our wheelchair ramp calculator does: you provide the rise, and it returns the precise minimum length using the 1:12 slope. This ensures a gentle enough incline for manual wheelchairs and most mobility scooters.
Why does one ratio fit so many cases? A 1:12 slope yields a roughly 4.8° angle – gentle enough to prevent tipping, but still short enough to be practical for most homes. Steeper slopes (like 1:8) are sometimes used for very short rises, but the ADA and most building codes recommend the 1:12 ratio whenever possible. If your rise is over 30 cm (12 inches), you may even need a landing platform. Our ADA ramp length calculator gives you the baseline figure instantly – ideal for architects, DIY builders, and caregivers. Use it before you buy materials; the result tells you exactly how many feet or meters of ramp module you need.
Remember: the ramp length from rise is only part of the design. You still need to account for the platform at top/bottom, handrails if rise exceeds 15 cm, and width – usually at least 36 inches (91 cm) clear. But this tool answers the most important question: “what is the minimum ramp length for my rise?” Bookmark it for planning any access project.