About ADA Ramp Slope Calculator
The ADA ramp slope calculator designs wheelchair ramps to the 2010 ADA Standards for Accessible Design and ICC A117.1. In design mode, enter the total vertical rise and a running slope preset - 1:12 is the ADA maximum for new construction, while 1:16 and 1:20 are the preferred, easier-to-use slopes - and the tool returns the required horizontal run, the number of intermediate landings from the 30 in (760 mm) maximum rise per run, the 60 in (1525 mm) landing lengths, and the total ramp footprint.
In check mode, enter the rise and the run you actually have and the calculator reports the resulting slope as a 1:x ratio, percent, and degrees, then grades it against the ADA 1:12 new-construction maximum with the run margin, the existing-site exceptions of 1:10 for a rise up to 6 in and 1:8 for a rise up to 3 in (ADA 405.2 Exception), and the IBC 1012.2 means-of-egress limit. Handrail requirements (rise over 6 in per ADA 405.8) and the 1:48 maximum cross slope are flagged throughout.
How It Works
- Pick design or check mode and enter the total vertical rise in inches or millimetres.
- Design mode: choose a slope preset (1:12 ADA maximum, 1:16 or 1:20 preferred, or the 1:10 / 1:8 existing-site exceptions limited to 6 in / 3 in of rise) and the tool computes run = rise x slope factor.
- Intermediate landings are added from the 30 in maximum rise per run: landings = ceil(rise / 30) - 1, each 60 in long, with optional 60 in top and bottom landings for the full footprint.
- Check mode: enter the available run and the calculator returns the actual slope 1:x, percent, and degrees, then compares it against the ADA 1:12 limit with the run margin and the existing-site exceptions.
Worked Example
A porch sits 36 in (914 mm) above grade. At the ADA maximum slope of 1:12 the required sloped run is 36 x 12 = 432 in = 36 ft. Because the rise exceeds the 30 in maximum per ramp run, ceil(36 / 30) - 1 = 1 intermediate landing of 60 in is required, so the ramp footprint is 432 + 60 = 492 in (41 ft), plus 60 in top and bottom landings if included in the layout. The slope is 8.33 % (4.76 degrees), and because the rise exceeds 6 in, handrails are required on both sides per ADA 405.8.
Formulas
- Required run at slope 1:x
run = rise * x- Slope ratio, percent and angle
1:x = run / rise; slope % = 100 * rise / run; angle = atan(rise / run)- Intermediate landings (ADA 405.6)
landings = ceil( rise / 30 in ) - 1- Total horizontal footprint
L_total = run + 60 in * landings [+ 2 * 60 in end landings]
Standards & References
- 2010 ADA Standards for Accessible Design section 405 (ramps)
- ICC A117.1 Accessible and Usable Buildings and Facilities
- IBC 1012.2 ramps in means of egress (max slope 1:12)
Frequently Asked Questions
What is the maximum ADA ramp slope?
The 2010 ADA Standards limit the running slope of a new ramp to 1:12, meaning one inch of rise for every 12 inches of run, which is 8.33 % or about 4.76 degrees. Shallower slopes of 1:16 to 1:20 are recommended wherever space allows because they are much easier for manual wheelchair users to climb. The cross slope perpendicular to the direction of travel is limited to 1:48.
How long does a wheelchair ramp need to be?
At the 1:12 maximum you need one foot of ramp for every inch of rise, so a 30 in rise needs a 30 ft sloped run. If the rise exceeds 30 in (760 mm), the run must be broken with intermediate level landings at least 60 in (1525 mm) long, and level landings are also required at the top and bottom. The total footprint is therefore the sloped run plus all landings - this calculator adds them up for you.
When are steeper slopes like 1:10 or 1:8 allowed?
Only on existing sites, buildings, or facilities where space limitations prevent a 1:12 slope (ADA 405.2 Exception). A slope between 1:10 and 1:12 is permitted for a maximum rise of 6 in (150 mm), and a slope between 1:8 and 1:10 is permitted for a maximum rise of 3 in (75 mm). A slope steeper than 1:8 is never permitted, and these exceptions do not apply to new construction.
When does a ramp need handrails and edge protection?
ADA 405.8 requires handrails on both sides of any ramp run with a rise greater than 6 in (150 mm). Handrails must be 34 to 38 in above the ramp surface with extensions at the top and bottom. Ramps with drop-offs also need edge protection - a curb, barrier, or extended surface - so wheelchair casters and crutch tips cannot slip off the side (ADA 405.9).
How many landings does my ramp need?
ADA 405.6 limits the rise of any single ramp run to 30 in (760 mm), so a rise of 36 in needs at least two runs separated by one intermediate landing, computed as ceil(rise / 30) - 1. Every landing must be at least as wide as the ramp and at least 60 in (1525 mm) long, and landings where the ramp changes direction must be at least 60 x 60 in. Level landings are also required at the top and bottom of every run.
Is the ADA slope limit the same for egress and residential ramps?
Ramps that are part of a means of egress are limited to 1:12 by IBC 1012.2, matching the ADA, while other pedestrian ramps under the IBC may be as steep as 1:8. The IRC allows residential ramps up to 1:8 where not serving an accessible route, though 1:12 remains the accessibility benchmark. Always check the code adopted by your local jurisdiction before building steeper than 1:12.