What is the 1:12 rule?
The ADA maximum ramp slope is 1 unit of rise per 12 units of run -- a direct code citation, same tier as this app's other direct code citations (e.g. the 4 in guardrail-opening rule).
Ramp Calculator
Ramp run and length from rise, checked against the ADA 1:12 maximum slope.
Enter a rise to plan the ramp.
Ramp inputs
Enter rise. Leave run blank to compute the minimum run at the ADA 1:12 max slope, or enter a run to check its slope. Rise above 30 in is more than one ramp run.
Enter a rise to plan the ramp.
Plan for
Ramp results
Warnings
- ERROR Enter a rise greater than zero.
Detail values
- Run used (sloped surface, landings excluded)
- — ft
- Ramp length (sloped surface, landings excluded)
- — ft
- Slope
- —
- Meets ADA 1:12 max slope (405.2)
- —
- Meets ADA 30 in max rise per run (405.6)
- —
- Ramp runs required
- —
- Handrails required, both sides (405.8, 505.2)
- —
Assumptions
- Max slope: 1:12 (ADA 405.2)
- Max rise per ramp run: 30 in (ADA 405.6)
- Landing between runs: 60 in minimum length (ADA 405.7.3) -- not counted in the run or length
- Handrails: Both sides once the rise is greater than 6 in (ADA 405.8, 505.2), each extended 12 in beyond the top and bottom of every run (ADA 505.10.1)
- Residential ramps: IRC R311.8.1 sets the same 1:12 maximum for the ramp serving a dwelling's required egress door. Other residential ramps, and any ramp where site constraints make 1:12 technically infeasible, may go to 1:8 under that section -- this screen checks the ADA figure and never applies the 1:8 allowance.
Included: ramp run and length (sloped surface only), ADA 1:12 slope check (405.2), ADA 30 in max rise per run (405.6), handrail footage, both sides with 12 in extensions (405.8, 505.2, 505.10.1).
Not included: labor, permits, engineering review or stamped plans, fasteners and connectors unless explicitly itemized above. Also not included: landing framing or surface (ADA 405.7.3 sets it at 60 in minimum length and this screen does not size it), cross slope (405.2 caps it at 1:48), edge protection (405.9).
Formula details
- Minimum run: rise x 12
ADA 405.2: the running slope of a ramp shall not be steeper than 1:12.
- Ramp length: sqrt(rise^2 + run^2)
- Slope ratio: rise / run
- Ramp runs required: ceil(rise / 30 in)
ADA 405.6: each ramp run shall have a rise of 30 in maximum. ADA 405.7.3 sets the landing between runs at 60 in minimum length, and that horizontal distance is additional to the run figure.
- Handrail: 2 sides x (ramp length + 2 x 12 in extension per run)
ADA 405.8 requires handrails once the rise is greater than 6 in, 505.2 puts them on both sides, and 505.10.1 extends each 12 in minimum horizontally beyond the top and the bottom of every ramp run. NOT included: rail carried along the full length of an intermediate landing, which 505.3 requires only where runs switch back -- this screen never asks how the runs are arranged, so the figure is the minimum for a straight climb.
Material List
About this calculator
Enter rise. Leave run blank to get the minimum ADA-compliant run, or enter your own run to check its slope.
FAQ
What if I already know my run?
Enter it, and CrewMeasure checks whether the resulting slope meets 1:12 -- if it's steeper, you'll see a warning with the minimum run needed for your rise.