Ramp Calculator · Slope, Ratio & ADA Compliance

Ramp Calculator

Enter rise and run to get slope, ratio, angle, ramp length & ADA compliance

Ramp Dimensions
Rise = total vertical height the ramp must climb · Run = horizontal length from bottom to top.
Common Slope Presets
Clicking a preset recalculates Run from the current Rise while keeping the chosen slope ratio.
Ramp Analysis
✅ ADA Compliant
Ramp Slope
—
—
Slope Ratio
—
Angle
—
Ramp Length
—
ADA Min Length
—
📐 Slope Ratio (Run : Rise)
1 : — rise units per run unit
📋 ADA Compliance & Recommendation
Enter the ramp rise and run to see the slope and compliance details.
📊 Ramp Slope Reference
Slope
Ratio
Typical Use
≤ 5%
1:20 or flatter
Comfortable for wheelchairs & walkers.
5% – 6.67%
1:20 to 1:15
Very accessible, long ramp footprint.
6.67% – 8.33%
1:15 to 1:12
ADA compliant for new construction.
8.33% – 10%
1:12 to 1:10
Steep — only for existing sites.
10% – 12.5%
1:10 to 1:8
Very steep — maximum for existing sites only.
> 12.5%
Steeper than 1:8
Not a safe ramp. Redesign required.
ADA also requires landings (min. 5 ft × 5 ft) at the top and bottom of every ramp run, and landings every 30 ft (9.1 m) of run, plus edge protection and handrails on ramps with rise > 6 in (150 mm).

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Faiq Ur Rahman

Founder & CEO, Toolraxy

Faiq Ur Rahman is a web designer, digital product developer, and founder of Toolraxy, a growing platform of web-based calculators and utility tools. He specializes in building structured, user-friendly tools focused on health, finance, productivity, and everyday problem-solving.

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Introduction

Accessible ramps live or die by a single number: their gradient. Push it too steep and a wheelchair user cannot manage the climb unaided, a walker loses confidence on the descent, and a building inspector signs off with a rejection notice. The ADA draws a hard line at 1:12 for new accessible routes, but working out whether a given rise and run actually hit that mark involves four interlocking figures, percentage, ratio, angle and surface length and converting between them by hand is where most mistakes creep in. This ramp calculator does all four at once. It is built for contractors checking a design before ordering materials, for homeowners planning a ramp for a family member, and for anyone who needs to confirm that a slope they have measured on site is genuinely usable.

 

How to Use the Ramp Calculator

  1. Measure the vertical distance between the lower and upper surfaces and type it into the Rise field.

  2. Pick the unit that matches your tape from the dropdown.

  3. Measure the horizontal distance from the foot of the ramp to its top, then enter it as the Run.

  4. Confirm the run unit — mixing feet and inches here is a common source of error.

  5. Watch the large slope figure update, with the ratio and angle printed immediately below it.

  6. Read the status badge for an immediate compliance verdict.

  7. Scan the four summary tiles for ratio, angle, surface length and the ADA-minimum length for that rise.

  8. Try a preset such as 1:20 · 5% to see how the run would change, or hit Reset to restore the defaults.

 

How the Ramp Calculator Formula Works

The tool treats the ramp as the hypotenuse of a right triangle and derives every output from the rise and run you supply. Nothing is estimated, weighted or approximated — the geometry is exact, and the only judgement call is the ADA comparison at the end.

Formula: Slope (%) = (Rise ÷ Run) × 100
Formula: Ratio = 1 : (Run ÷ Rise)
Formula: Angle = atan(Rise ÷ Run) in degrees
Formula: Surface Length = √(Rise² + Run²)
Formula: ADA Minimum Length = √(Rise² + (12 × Rise)²)

Both inputs must be greater than zero. If either is blank, zero or negative, the results panel replaces every figure with a prompt rather than showing a misleading number. The ADA minimum length assumes the flattest permitted gradient, 1:12, and reports how long the ramp surface would need to be if you extended the run to satisfy it, a useful target when you are deciding whether to redesign or seek an exception.

 

Worked Example

A homeowner is replacing a 250 mm step at a side entrance. The available run from the door to the garden path is 3.6 m.

  • Rise = 250 mm = 0.25 m

  • Run = 3.6 m

  • Slope = (0.25 ÷ 3.6) × 100 = 6.94%

  • Ratio = 1 : (3.6 ÷ 0.25) = 1 : 14.40

  • Angle = atan(0.25 ÷ 3.6) = 3.98°

  • Surface length = √(0.25² + 3.6²) = 3.61 m

  • ADA minimum length for a 250 mm rise = √(0.25² + 3.0²) = 3.01 m

At 6.94% the ramp is comfortably under the 8.33% ceiling, so the badge reads ADA Compliant. Note that the ADA minimum length is shorter than the actual surface length that is because the available run is longer than strictly necessary, which means the ramp is gentler than the code requires. The takeaway: a 250 mm step needs a minimum run of 3.0 m at 1:12, and this design has 3.6 m, giving a margin of comfort that is worth having on an outdoor ramp exposed to rain.

Mistakes That Throw Off Ramp Slope Calculations

  • Measuring along the slope instead of horizontally for the run.

  • Ignoring a threshold or second step when recording the rise.

  • Treating 1:12 as a target to hit rather than a ceiling to stay under.

  • Forgetting the 760 mm cap on rise per continuous run, which forces intermediate landings.

  • Overlooking handrail requirements once the rise passes 150 mm.

  • Mixing units without converting, six inches of rise against six feet of run is not the same as six inches against six inches.

  • Assuming a compliant slope alone makes the ramp legal, when width, landings and edge protection also apply.

 

Putting It Together: A Deck Ramp Scenario

A homeowner needs to reach a deck whose surface sits 22 inches above the lawn. The obvious plan is a straight ramp across 12 feet of garden. Entering 22 in rise and 12 ft run gives 144 inches of run, a gradient of 15.28%, and a “Dangerous, not a ramp” badge. The calculator also shows that 1:12 would demand a run of 264 inches, 22 feet which does not fit the garden at all. That single comparison reframes the project: the realistic answer is a switchback ramp with an intermediate landing, or a different access route entirely, rather than a straight run across the lawn.

 

Benefits of Using This Ramp Calculator

  • Produces four separate geometric outputs from two inputs, eliminating repeated manual trigonometry.

  • Gives an immediate ADA verdict in plain language, so a design can be screened before any materials are ordered.

  • Accepts metric and imperial measurements in any combination, which suits drawings that mix feet with millimetres.

  • Performs every calculation in the browser, so no site dimensions or project details are ever transmitted.

  • Behaves identically on a phone held on site and a desktop in the office.

  • Offers one-tap presets for the five ratios that come up most often in accessibility work.

  • Ships with worked examples covering a small step, a wheelchair-height rise and an imperial measurement, so a full result is visible without typing anything.

 

Frequently Asked Questions

What ratio does a 1:12 slope represent?

It means one unit of vertical rise for every twelve units of horizontal run. In percentage terms that is 8.33%, and as an angle it works out at approximately 4.76°. It is the steepest gradient the ADA allows for a new ramp on an accessible route.

 

How long does a ramp need to be for a given height?

Multiply the rise by twelve. A 300 mm step needs 3,600 mm of run at 1:12; a 500 mm step needs 6,000 mm. Add landings at both ends on top of that figure, since landings are level areas and do not count toward the ramp run.

 

Why does the calculator mark my ramp as non-compliant?

The most common reason is a gradient above 8.33%. The second most common is a rise greater than 760 mm in a single continuous run, which the tool flags separately even when the slope itself is fine that situation requires intermediate landings or splitting the ramp into separate runs.

 

What is the difference between slope percentage and slope ratio?

They describe the same incline in different units. Percentage is rise divided by run, multiplied by 100. Ratio is run divided by rise, written as 1:X. A 1:12 ramp is 8.33%; a 1:20 ramp is 5%. Percentage is common in engineering and drainage work, while ratio dominates accessibility codes.

 

What angle does an 8.33% ramp correspond to?

Approximately 4.76 degrees. The relationship is not linear doubling the percentage does not double the angle so it is worth letting the calculator handle the conversion rather than estimating.

 

Do short ramps still need landings?

Yes, if the rise exceeds 760 mm within a single run, or if the ramp changes direction. A very short ramp serving a small step with a level area already present at both ends may not need additional constructed landings, but the level area itself still has to meet the minimum dimensions.

 

Can I use this tool for a vehicle ramp or a driveway slope?

The geometry is identical, so the slope, ratio, angle and length figures are valid for any inclined surface. The ADA compliance badge, however, refers specifically to pedestrian accessible routes and does not reflect vehicle ramp standards or local driveway regulations.

 

How do I convert a rise measured in inches to metres?

Multiply inches by 0.0254. The calculator does this internally, so you can simply select inches from the rise dropdown and leave the number as measured. If you change the unit after typing, the value is converted automatically so the physical measurement stays the same.

 

Is a flatter ramp always better?

Flatter ramps are easier to use and safer in wet conditions, but they consume far more horizontal space. A 1:20 ramp needs nearly twice the run of a 1:12 ramp for the same rise. The practical answer is usually the steepest gradient you can comfortably accommodate, provided it stays at or below 1:12.

 

When are handrails mandatory on a ramp?

Once the rise exceeds 150 mm, handrails are required on both sides. They must run continuously along the ramp and its landings, and they must meet specified height and grip requirements. The calculator does not check handrails, so treat them as a separate compliance item.

 

Does this tool calculate the number of landings required?

No. It flags when a rise exceeds the 760 mm single-run limit, which is the trigger for intermediate landings, but it does not work out how many landings a given design needs. That depends on the total run and how the ramp is laid out.

Disclaimer

The ramp calculator produces geometric results and an indicative ADA comparison for planning purposes only. It is not a substitute for a professional accessibility survey, a structural assessment or a review against your local building code. ADA requirements and their local adoptions change, and existing-site exceptions are granted at the discretion of the relevant authority. Confirm all figures with a qualified designer or your local code office before beginning construction.

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