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Construction & Home
Wheelchair Ramp Calculator — ADA Ramp Length & Slope
ADA ramp length, slope percent and landings for any rise (1:12, 1:16, 1:20)
A wheelchair ramp calculator answers the one question that decides whether a ramp is safe and code-legal: how long does the ramp have to be for the height I need to climb? Get it wrong and the ramp is too steep to roll up, fails inspection, or won't physically fit the yard. This tool uses the ADA (Americans with Disabilities Act) 1:12 rule to turn a single measurement — the rise, or total vertical height from the lower level to the doorway or landing — into ramp length, slope percentage, and the number of level landings the run requires.
The rule itself is simple and worth memorizing. ADA sets the maximum running slope of a ramp at 1:12. That means for every 1 inch of vertical rise, you need 12 inches (1 foot) of ramp run. So a 24-inch rise needs 24 feet of ramp; a 30-inch rise needs 30 feet. In ratio terms 1:12 works out to an 8.33% slope (1 ÷ 12 × 100), which is the steepest a compliant ramp is allowed to be.
Gentler ratios are often required or recommended. A 1:16 slope (6.25%) is the comfortable target for occupied wheelchairs and for ramps people use unassisted; a 1:20 slope (5%) is so gradual it isn't even classified as a ramp under ADA and needs no handrails. The trade-off is length: at 1:16 a 24-inch rise needs 32 feet of ramp, and at 1:20 it needs 40 feet. This calculator lets you pick the ratio and shows the length each one demands so you can balance comfort against the space you actually have.
Length (ft) = rise (in) × slope ratio ÷ 12. At 1:12 that simplifies to length in feet equals the rise in inches (24 in → 24 ft). The slope percentage back-checks the design: slope% = rise ÷ (length × 12) × 100.
Two ADA limits drive the rest of the layout. First, a single ramp run is capped at 30 inches of rise — no more than 30 ft of horizontal run before you must break the ramp. Second, you need a level landing every 30 inches of rise, and at the top and bottom, each landing at least 60 inches long so a chair can rest, turn or open a door. A 36-inch rise therefore can't be one straight ramp: it needs at least one intermediate landing, splitting the climb into two runs. This calculator flags when your rise crosses that threshold and tells you how many landings to plan, so the design you price out is the design that passes inspection.
📖 See also: How to Calculate a Tip (and Split the Bill)
Calculator
Fill in the fields and click "Calculate" for instant results.
📰 Formula
• Ramp length (ft) = rise (in) × slope ratio ÷ 12 • At 1:12, length in feet = rise in inches (1 in rise per 1 ft run) • Slope percentage = rise ÷ (length × 12) × 100 • Slope ratios and grades: 1:12 = 8.33% (ADA maximum) · 1:16 = 6.25% · 1:20 = 5.0% • ADA single-run limit: no more than 30 in of rise (about 30 ft of run) per ramp run • Landings: one level landing every 30 in of rise; top and bottom landings at least 60 in long
📰 Formula
• Ramp length (ft) = rise (in) × slope ratio ÷ 12 • At 1:12, length in feet = rise in inches (1 in rise per 1 ft run) • Slope percentage = rise ÷ (length × 12) × 100 • Slope ratios and grades: 1:12 = 8.33% (ADA maximum) · 1:16 = 6.25% · 1:20 = 5.0% • ADA single-run limit: no more than 30 in of rise (about 30 ft of run) per ramp run • Landings: one level landing every 30 in of rise; top and bottom landings at least 60 in long
🧪 Worked examples
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Example 2
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Example 3
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Example 4
⚠️ Common mistakes
- Reading the rise in feet instead of inches — a 2 ft (24 in) step needs 24 ft of ramp, not 2 ft.
- Assuming any ramp is fine; anything steeper than 1:12 (8.33%) fails ADA for public use.
- Forgetting that rise over 30 inches must be broken into multiple runs with a landing between.
- Leaving out the top and bottom landings (each at least 60 in long) when measuring the total footprint.
- Confusing slope ratio with slope percent — 1:12 is the ratio, 8.33% is the same slope as a grade.
💡 Tips
- If you have the room, build to 1:16 (6.25%) — it's far easier to roll up than the 1:12 maximum.
- 1:20 (5%) needs no handrails under ADA but is the longest; reserve it for low rises with lots of space.
- Measure rise from the finished lower surface to the top landing, not to the threshold lip.
- Add the 60-inch top and bottom landings to the ramp run to get the real footprint your yard must fit.
- For an occupied chair pushed by a helper, 1:12 is workable; for self-propelling, aim gentler than 1:12.
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Copy the code below and paste it into the HTML of your site or blog.
<iframe src="https://www.calcnimbus.com/embed/ramp-calculator" width="100%" height="500" frameborder="0" style="border:1px solid #eee;border-radius:12px"></iframe>
❓ Frequently asked questions
How long does a wheelchair ramp need to be?
Use the ADA 1:12 rule: for every 1 inch of rise you need 12 inches (1 foot) of ramp. So measure the total height (rise) in inches and that equals the ramp length in feet — a 24-inch rise needs 24 feet of ramp.
What is the ADA maximum slope for a ramp?
ADA sets the maximum running slope at 1:12, which is an 8.33% grade. That is the steepest a compliant ramp may be. Gentler slopes such as 1:16 (6.25%) or 1:20 (5%) are easier to use but require more length.
What does a 1:12 ramp slope mean?
1:12 means 1 unit of vertical rise for every 12 units of horizontal run — 1 inch up for every 12 inches (1 foot) forward. Expressed as a percentage it is 1 ÷ 12 × 100 = 8.33%, the ADA maximum slope.
How do I calculate ramp slope as a percentage?
Slope percent = rise ÷ run × 100, with rise and run in the same units. A 24-inch rise over a 288-inch (24 ft) run is 24 ÷ 288 × 100 = 8.33%, which matches the 1:12 ratio.
How long should a ramp be for a 2-foot rise?
A 2-foot rise is 24 inches. At the ADA 1:12 slope that needs 24 feet of ramp. At a gentler 1:16 it needs 32 feet, and at 1:20 it needs 40 feet. Add level landings at the top and bottom.
When does a wheelchair ramp need a landing?
ADA requires a level landing every 30 inches of vertical rise, and a landing at the top and bottom of every ramp. Each landing must be at least 60 inches long so a wheelchair can rest, turn or open a door.
What is the maximum rise for a single ramp run?
Under ADA a single ramp run may not exceed 30 inches of rise, which is about 30 feet of run at 1:12. A taller rise must be split into multiple runs separated by level landings.
Is a 1:12 ramp the same as a 1:16 or 1:20 ramp?
No. They are different slopes. 1:12 (8.33%) is the ADA maximum and the steepest allowed. 1:16 (6.25%) and 1:20 (5%) are gentler and easier to climb but need more horizontal length for the same rise.
Do all wheelchair ramps need handrails?
Under ADA, ramps with a rise greater than 6 inches need handrails on both sides. A slope of 1:20 (5%) or gentler is technically a sloped walkway, not a ramp, and does not require handrails.