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Ramp Slope Calculator

Run, ramp length, angle and slope percent from the rise, checked against the ADA 1:12 limit with the landings a long ramp needs.

Ramp Dimensions

Height from the lower surface to the upper surface

Fill this in to check the slope of an existing or space-limited ramp

Tip

Measure the rise with a level and tape from where the ramp will start, not from the bottom step: ground that falls away from the building adds rise.

Results

Run (horizontal)

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Ramp surface length

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Angle

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Slope

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Ratio (rise : run)

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Straight footprint incl. landings

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ADA slope check

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Runs and landings (30 in max rise per run)

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Ramp Profile

How ramp slope is calculated

A ramp is a right triangle lying on its side: the rise is the vertical leg, the run is the horizontal leg, and the walking surface is the hypotenuse. Slope is rise ÷ run, and the three ways of writing it (ratio, percent and degrees) are conversions of that one number.

run = rise × ratio (rise × 12 for a 1:12 ramp)

ramp length = √(rise² + run²)

angle = arctan(rise ÷ run)

slope % = rise ÷ run × 100

Worked example: a 24 in rise at 1:12

  1. Run = 24 × 12 = 288 in = 24 ft.
  2. Ramp surface = √(24² + 288²) = √83,520 = 289.0 in (24' 1").
  3. Angle = arctan(24 ÷ 288) = 4.76°; slope = 8.33%.
  4. The rise is under 30 in, so one run is enough. With 60 in landings top and bottom, the straight footprint is 288 + 120 = 408 in = 34 ft.
  5. The rise is over 6 in, so handrails are required on both sides.

Slope ratios compared

RatioAnglePercentRun per 1 in of riseWhere it applies
1:87.13°12.50%8 inExisting buildings only, rise up to 3 in
1:105.71°10.00%10 inExisting buildings only, rise up to 6 in
1:124.76°8.33%12 inADA maximum for new ramps
1:163.58°6.25%16 inComfortable for manual wheelchairs
1:202.86°5.00%20 inAnything gentler is a walkway, not a ramp

1:12 ramp sizes by rise

RiseRunRamp surface (ft)Runs neededStraight footprint with landings
6 in6 ft6.02116 ft
12 in12 ft12.04122 ft
18 in18 ft18.06128 ft
24 in24 ft24.08134 ft
30 in30 ft30.10140 ft
36 in36 ft36.12251 ft
48 in48 ft48.17263 ft
60 in60 ft60.21275 ft

Footprint = run + a 60 in landing at the bottom, the top, and between runs. Switchback and L-shaped ramps need 60 × 60 in turning landings instead.

ADA ramp requirements at a glance

  • Running slope: 1:12 (8.33%) maximum. Cross slope: 1:48 maximum.
  • Rise per run: 30 in maximum before a level landing.
  • Landings: top and bottom of each run, at least 60 in long and as wide as the ramp; 60 × 60 in where the ramp changes direction.
  • Clear width: 36 in minimum between handrails.
  • Handrails: both sides when the rise exceeds 6 in. Edge protection (a curb or extended surface) on open sides.

These figures come from section 405 of the 2010 ADA Standards for Accessible Design. The ADA applies to public and commercial facilities; for a private home your local residential code governs, and many jurisdictions adopt the same numbers. Confirm with your building department before you build.

The same triangle math drives the roof pitch calculator and the stair stringer calculator. To solve any other right triangle from two known values, use the right triangle calculator.

Frequently Asked Questions

How long does a wheelchair ramp need to be?

At the ADA maximum slope of 1:12 you need 12 inches of run for every inch of rise. A 24 in rise (about three steps) needs 288 in, or 24 ft, of sloped run. Add a 60 in landing at the top and bottom and the straight-line footprint is 34 ft.

What is a 1:12 slope in degrees and percent?

A 1:12 slope is arctan(1/12) = 4.76° and 1 ÷ 12 = 8.33%. Ratio, angle and percent all describe the same steepness: percent is rise ÷ run × 100, and the angle is the inverse tangent of rise ÷ run.

When does a ramp need a landing?

Under the 2010 ADA Standards (section 405) a single ramp run may rise no more than 30 in, which is 30 ft of run at 1:12. Taller ramps are split into runs with a level landing between them. Landings are also required at the top and bottom of every run and wherever the ramp changes direction, where they must be at least 60 × 60 in.

Is the ramp length the same as the run?

Not quite. The run is the horizontal distance; the ramp surface is the hypotenuse, √(rise² + run²). At 1:12 the difference is small (a 288 in run has a 289 in surface), but it grows quickly on steeper ramps such as loading or shed ramps, so order decking from the sloped length.

Can a ramp be steeper than 1:12?

Not for new ADA-covered construction. The ADA Standards allow 1:10 for a rise of up to 6 in and 1:8 for a rise of up to 3 in only in existing buildings where space is limited. Private homes are not covered by the ADA, but 1:12 is still the practical limit for an unassisted manual wheelchair user, and 1:16 to 1:20 is noticeably easier.

Do I need handrails?

ADA requires handrails on both sides of any ramp run with a rise greater than 6 in. They must be 34 to 38 in above the ramp surface and extend 12 in horizontally beyond the top and bottom of the run. Always confirm with your local building department, which may have stricter rules.

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