Wheelchair Ramp Slope Calculator

By Uzair Arshad , Senior Civil and Structural Engineer

Last updated: April 26, 2026

Use this wheelchair ramp slope calculator to convert a doorway or step rise into horizontal run, ramp surface length, slope ratio, percent grade, and angle. Homeowners planning a residential wheelchair ramp, contractors, and DIY builders can check an existing ramp or plan a new one with ADA-style guidance before ordering materials. Enter measurements in inches, feet, centimeters, or meters.

How to use this calculator

This wheelchair ramp slope calculator helps you plan a new ramp or verify an existing one. It converts your rise measurement into run, ramp surface length, slope ratio, percent grade, and angle so you can check feasibility before buying materials or calling contractors.

Measure the vertical rise from the lower surface to the finished landing or doorway threshold. Measure after any finish flooring, mats, or threshold plates are in place because even 1 inch of extra rise adds 1 foot of run at a 1:12 slope.
Choose your calculation mode. Use Find ramp length when planning a new build, or Check existing ramp to verify the slope of a ramp already in place.
Select a common ratio (1:12, 1:16, or 1:20) or enter a custom value. A 1:12 slope is a common maximum guideline, while 1:16 or 1:20 creates a gentler, easier push for manual wheelchair users.
Review the results: horizontal run, ramp surface length, slope ratio, grade percentage, angle, and the ADA-style planning note together.

Pro tip: measure at three different points and average them. Uneven ground, settled concrete, or sloped walkways mean actual rise varies across the doorway width. Averaging prevents ordering a ramp that's too short on one side.

Common mistake: measuring from the bottom of the door trim instead of the finished walkway surface. Always measure from the ground you'll actually roll on to the top landing surface.

Metric support: this residential wheelchair ramp slope calculator accepts rise and run in inches, feet, centimeters, or meters. All outputs display in feet-and-inches with an equivalent in your chosen unit when you select centimeters or meters.

Quick slope ratio reference

Use this table to compare how rise translates to run at different slope ratios before entering your numbers.

Slope ratio	Grade (%)	Run per 1 in rise	Use case
1:12	8.33%	12 in	Common ADA maximum for new construction ramps.
1:16	6.25%	16 in	Gentler grade for manual wheelchair users and seniors.
1:20	5.00%	20 in	Very gentle route, good for long outdoor paths.

A DIY builder should compare all three ratios because choosing 1:20 over 1:12 nearly doubles the required yard or garage space for the same rise.

How the calculation works

Geometry:
Run = Rise × Ratio Denominator
Ramp Surface Length = √(Rise² + Run²)

Slope:
Slope Grade (%) = (Rise / Run) × 100
Slope Angle (°) = arctan(Rise / Run) × 180 / π

Ratio:
Slope Ratio = 1 : (Run / Rise)

Rise: Vertical height from the lower surface to the landing or doorway threshold
Run: Horizontal distance the ramp covers, excluding landings
Ratio Denominator: The X in a 1:X slope ratio (e.g. 12 for a 1:12 ramp)
Ramp Surface Length: Actual length of the ramp board along the slope (hypotenuse)
Slope Grade: Rise divided by run, expressed as a percentage
Slope Angle: Incline angle in degrees

This wheelchair ramp slope calculator uses three core relationships between rise, run, and ramp surface length to give you slope ratio, percent grade, and angle in one step.

Core formulas

Horizontal run: Multiply rise by the ratio denominator. For a 1:12 slope, every inch of rise needs 12 inches of run.

Ramp surface length: Use the Pythagorean theorem: √(Rise² + Run²). This gives the actual board length along the slope, which is always slightly longer than the horizontal run.

Slope grade: Divide rise by run and multiply by 100. A 1:12 slope equals 8.33% grade.

Slope angle: Use arctan(Rise / Run) and convert from radians to degrees. A 1:12 slope is about 4.76 degrees.

Worked example

Given: 24 inch rise at a 1:12 target ratio.

Run = 24 × 12 = 288 inches = 24 feet
Ramp surface length = √(24² + 288²) = √(576 + 82,944) = √83,520 = 288.99 inches = 24 ft 1.0 in
Slope grade = (24 / 288) × 100 = 8.33%
Slope angle = arctan(24 / 288) × 180 / π = 4.76 degrees

That 24 feet of horizontal run does not include landings. Add at least 5 feet at top and bottom for a total site footprint of about 34 feet.

Check existing ramp mode

If you already have a ramp and want to verify its slope, enter the rise and the measured horizontal run. The calculator divides run by rise to find the ratio denominator, then shows grade, angle, and an ADA-style check. This is useful when buying a home with an existing ramp or auditing a commercial property.

Assumptions and limitations

The 1:12 maximum running slope comes from ADA Standards for Accessible Design, Section 405.2, which applies to newly constructed ramps in commercial and public facilities. Residential codes vary by jurisdiction and may allow steeper slopes in some retrofit situations. Always confirm with your local permit office before construction.

This calculator handles slope geometry only. It does not design landings, handrails, ramp width, surface material, drainage, or edge protection. Those elements are controlled by local building codes, and requirements vary between residential and commercial projects.

Mats, pavers, settled concrete, and door threshold plates can change the final rise enough to affect ramp length. Always measure to the finished surface, not the framing or subfloor. Outdoor ramps also need clearance for drainage, snow buildup, and a non-slip surface finish.

For a detailed walkthrough of ramp run, length, and grade formulas, see our guide on how to calculate ramp length from rise. For a plain-language explanation of the 1:12 rule, see our ADA ramp slope guide.

Frequently Asked Questions

How to calculate wheelchair ramp slope

Divide rise by run to calculate wheelchair ramp slope, then convert it to a ratio, percentage, or angle. For example, a 24 inch rise with a 288 inch run equals 1:12, 8.33%, and about 4.76 degrees. This calculator shows all three formats so you can compare plans quickly.

How to calculate ramp slope percentage for a wheelchair ramp

Use rise / run × 100 to calculate ramp slope percentage. A 12 inch rise over 144 inches of run gives 12 / 144 × 100, or 8.33%. Showing the percentage next to the 1:12 ratio helps you confirm the ramp meets accessibility guidelines at a glance.

What is the ADA slope for a wheelchair ramp?

A common ADA maximum running slope is 1:12, equal to about 8.33% grade or 4.76 degrees. Many wheelchair users prefer gentler slopes like 1:16 or 1:20 for easier self-propulsion. Local residential codes can differ from commercial ADA standards, so confirm with your permit office.

How long does a wheelchair ramp need to be for 3 steps?

Three standard steps (about 7.5 inches each) give roughly 22.5 inches of rise. At a 1:12 slope, you need about 22.5 feet of horizontal run plus top and bottom landing space. Measure actual step heights because risers vary from 6 to 8 inches across builders.