Ramp Calculator

Ramp Calculator results turn the rise to a door or porch into the run, landings and handrail length a wheelchair ramp needs, then test its slope against the ADA and IRC ramp rules.

Ramp Calculator for Wheelchair and Porch Ramps

A ramp is planned from one number, the rise. That is the vertical height from the ground to the top landing or door threshold, measured straight up rather than along the steps.

Families use the result to plan a wheelchair ramp at the front door, and builders use it to size decking, rails and landings before cutting anything. Facility managers use the check mode to see whether an older ramp still meets the ADA.

Most ramp tools stop at run length and angle. This Ramp Calculator also counts the runs and landings a tall rise needs, totals the straight footprint, sizes the deck surface and rails, and tells you which code rule the design passes or fails.

Design a New Ramp or Check One Already Built

Ramp Length Needed mode takes the total rise in inches and the standard you are building to. It returns the horizontal run in feet and inches, along with the slope it used and the sloped length along the surface.

Check an Existing Ramp mode adds the horizontal run you measured. It reports the slope as 1:X, the grade and the angle, then shows how much run the chosen standard needs and how far short of it the ramp falls.

The Standard menu covers ADA new construction, the two ADA slopes allowed at existing sites, the IRC egress ramp, other IRC home ramps and loading ramps. Width and landing length sit in the accordion at 36 and 60 inches by default, and the Units menu switches to centimeters and meters.

Run, Sloped Length and Angle From the Rise

A slope of 1:12 means 12 units of horizontal run for every unit of rise. Multiply the rise by the second number of the ratio to get the run, keeping both in the same unit.

$$Run=Rise\times X$$

With the rise in inches and a 1:12 slope, the run in inches divided by 12 gives feet, so a 24-inch rise needs 24 feet of run. That one-inch-per-foot shortcut works only at 1:12.

The ramp surface is a little longer than the run, because it is the hypotenuse of the triangle the rise and run form. The angle and grade come from the same triangle.

$$L_{sloped}=\sqrt{Ru{n}^2+Ris{e}^2}$$

$$\theta =\arctan \left(\frac{Rise}{Run}\right)$$

$$Grade=\frac{Rise}{Run}\times 100$$

A 1:12 slope works out to 4.76 degrees and an 8.33% grade. The most common mix-up is ordering a ramp by its horizontal run, since ramp kits are sold by their sloped deck length, which at 24 inches of rise is 24 feet 1 inch.

The fourth result card gives a field check you can do with a 2-foot level. Lay it on the ramp and the gap under its low end should equal 24 inches divided by X, which is 2 inches at 1:12.

ADA Ramp Rules the Calculator Checks

For public buildings and businesses, the 2010 ADA Standards set the limits in Section 405 of the U.S. Access Board text. A ramp run can be no steeper than 1:12, and no single run can climb more than 30 inches.

Steeper slopes are allowed only at existing sites where space rules out 1:12, and then only for short climbs. Table 405.2 sets the slope and rise pairs below, and the Ramp Calculator applies them when you pick an existing-site standard.

Each run needs a level landing at the top and bottom, at least 60 inches long and as wide as the ramp. Where the ramp turns at a landing, that landing must be at least 60 by 60 inches.

Runs with more than 6 inches of rise need handrails on both sides, and the rail length on the second card adds 12-inch extensions at the top and bottom. Clear width must be at least 36 inches between the rails.

A route at 1:20 or flatter is a walking surface rather than a ramp under the ADA, so those ramp rules no longer apply. That is why the slope table in the results lists 1:20 and 1:16 as options when space allows.

IRC Rules for a Ramp at a House

Private homes usually follow the International Residential Code rather than the ADA. Under R311.8.1 of the 2021 IRC, a ramp serving the required egress door can be no steeper than 1:12, while other ramps may reach 1:8.

The IRC calls for a landing at the top and bottom, where a door opens onto the ramp, and where it changes direction, with a width of at least 36 inches. A handrail is required on at least one side only when the ramp is steeper than 1:12, set 34 to 38 inches above the ramp surface.

Where rails are needed, the IRC wants them continuous for the full length of the ramp, with ends returned or stopped at newel posts. It has no 12-inch extension rule, so the rail length the calculator gives for an IRC ramp equals the sloped length.

The IRC sets that 36-inch landing width but no separate ramp width, so the card shows 36 inches as a suggestion at home rather than a code line. Local adoption varies, so confirm the rules with your building department before you build.

Taller Rises Need More Than One Run

Under the ADA, a 36-inch rise cannot be done in one run, because each run tops out at 30 inches. The first card splits it into 2 runs of 18 inches each, with 3 landings.

At 1:12 that is 36 feet of run, and the straight footprint grows to 51 feet once three 60-inch landings are added. The rails run continuously across the middle landing, so each side needs about 43 feet 1 inch of rail including both extensions.

The deck surface for a 36-inch-wide ramp comes to about 153 sq ft, counting the sloped runs and all three landings. Folding the same runs into an L or a switchback shortens the footprint, but each turn needs a 60 by 60 inch landing.

Checking a Ramp That Is Already Built

Say an existing ramp climbs 24 inches over 20 feet of horizontal run. Check mode reads that as 1:10, which the hero shows as a 10% grade at about 5.71 degrees.

That fails ADA new construction and the IRC egress rule, which both need 24 feet of run, so the ramp is 4 feet short. Its 20-foot run can serve at most 20 inches of rise at 1:12, while a non-egress IRC home ramp could stay as built.

If you only need the slope of a surface rather than a full ramp plan, the Ramp Slope Calculator works from rise and run alone. For keeping the steps beside a new ramp, the Stair Calculator handles risers and treads.

Loading Ramps for Mowers and Equipment

Loading or Equipment mode drops the access rules and lets you set any slope from the 1:2 to 1:6 presets or a custom value. The cards then show rise per foot and grade instead of landings and code checks.

Access codes don't cover equipment ramps, so the ramp maker's rated length, angle and weight capacity govern. Match those to the machine and the truck bed height before loading.

Ramp Length and Code Questions

How long does a ramp need to be for a 24-inch rise?

At the ADA and IRC egress slope of 1:12, a 24-inch rise needs 24 feet of horizontal run and about 24 feet 1 inch of ramp surface. That fits in one run, since it stays under the 30-inch ADA limit.

Add a 60-inch landing at each end and the straight footprint becomes 34 feet. The IRC sets a 36-inch landing width but no landing length, so a home ramp with shorter landings can fit a smaller footprint.

How long should a ramp be for 3 or 5 steps?

Measure the total rise and enter it in the Ramp Calculator instead of counting steps, because step heights vary. The IRC allows risers up to 7 3/4 inches, so 3 steps can rise about 23 inches and 5 steps about 39 inches.

At 1:12, a 39-inch rise needs about 38 feet 9 inches of run. That is over the 30-inch ADA limit for one run, so it needs two runs with a landing between them.

Do ramps at a private home have to meet the ADA?

The ADA governs public accommodations and commercial facilities, not single-family homes. Homes follow the IRC as adopted locally, which allows 1:12 at the egress door and 1:8 for other ramps.

Many families still build to 1:12 or gentler, because a 1:8 ramp is hard to climb in a manual chair without help. A wider, flatter ramp also suits walkers and visitors.

Does a ramp need handrails?

Under the ADA, any run with more than 6 inches of rise needs handrails on both sides, extending 12 inches past the top and bottom. Under the IRC, a home ramp needs a rail on at least one side only once it is steeper than 1:12.

A 1:12 home ramp can therefore be built without rails and still meet the IRC. Rails remain worth adding on any ramp used by someone who walks with a cane or walker.

What if there is no room for a 1:12 ramp?

Fold the ramp into an L or a switchback, with a 60 by 60 inch landing at each turn. At existing ADA sites with tight space, Table 405.2 allows 1:10 up to 6 inches of rise and 1:8 up to 3 inches.

A short 1:8 ramp over a 3-inch threshold needs only 2 feet of run. For tall porches where even a folded ramp won't fit, a vertical platform lift is the usual alternative.