Ramp Slope Calculator - Ratio, Percent, and Angle

A ramp slope calculator is a construction and DIY tool that turns a vertical rise and a horizontal run into the three ways a ramp slope is written on drawings, building forms, and code checks: a 1:N ratio, a percent grade, and an angle in degrees. The same inputs also feed an ADA 1:12 compliance flag, so the same result is usable for design work and for verifying an existing wheelchair ramp.

• • Wheelchair ramp design: Size the required run length for a 1:12 ADA ramp before ordering lumber or pouring concrete.
• • Threshold and porch ramp checks: Read the percent grade and angle of a short threshold ramp to confirm it is safe for a walker or scooter.
• • Driveway and garage floor slopes: Compare the slope of a new driveway or garage floor against typical drainage and ADA thresholds.
• • Loading dock and equipment ramps: Set the slope of an unoccupied equipment ramp against the 1:8 maximum used for carts and dollies.

The page accepts a rise and a run (or a rise and a target ratio) and returns the slope written in three units at once, so the same result is usable on a building plan, a code form, and an angle gauge.

When the goal is to size the full ramp layout, including landings and material takeoffs, the Ramp Calculator builds on the same 1:12 ADA logic and adds framing and lumber estimates.

The ramp slope is the ratio of vertical change to horizontal change between the start and the end of the ramp. The page takes your rise and run, divides rise by run, and writes the same result as a 1:N ratio, a percent grade, and an angle in degrees. The ADA flag is set when the ratio is 1:12 or shallower, which is the ADA maximum for new public wheelchair ramps.

• Vertical rise: Total vertical height the ramp must climb, in inches.
• Horizontal run: Total horizontal length of the ramp surface, in inches.
• Slope ratio: Run divided by rise, written in 1:N form so 12 means the ADA 1:12 standard.
• Slope percent: Vertical rise divided by horizontal run, multiplied by 100.
• Slope angle: Arctangent of rise over run, converted from radians to degrees.

The percent output is the decimal slope times 100, the angle is the arctangent of rise over run, and the ratio is the run divided by the rise. The ADA flag is set when the resulting ratio is at least 1:12, matching the ADA maximum for new public wheelchair ramps.

According to Omni Calculator ramp slope page, the ramp slope ratio equals run divided by rise, the slope percent equals (rise / run) * 100, and the slope angle in degrees equals atan(rise / run) * (180 / pi), with ADA compliance set when the ratio is at least 1:12.

The same rise over run division that returns a ramp slope also returns a roof pitch, and the Roof Pitch Calculator converts the pitch into the slope angle in degrees and a pitch multiplier in one step.

A ramp slope is one geometric idea that shows up under several names on drawings and codes. These four concepts cover the cases that come up most often on a real project.

Writing the result in 1:N form keeps the answer in the language an ADA inspector uses.

When the same rise and run describe a roof instead of a ramp, the Roof Slope Calculator uses the same percent and degree conversions and adds shingle and drainage rules on top.

Pick a calculation goal, enter the rise and run (or rise and target ratio), and read the slope as a ratio, a percent, an angle, and an ADA flag. The result panel updates as soon as any field changes.

1. 1 Pick the calculation goal: Select 'Find Ramp Slope' to read the slope of an existing ramp, or 'Find Required Ramp Length' to size a new ramp against a target ratio.
2. 2 Enter the vertical rise: Type the total vertical height the ramp must climb, in inches. For a 24 inch porch threshold, enter 24.
3. 3 Enter the horizontal run or target ratio: In slope mode, enter the horizontal run in inches. In length mode, enter the target ratio; 12 means the ADA 1:12 standard.
4. 4 Read the slope ratio, percent, and angle: The result panel shows the ratio (such as 1:12), the percent grade, and the slope angle in degrees, all from the same input pair.
5. 5 Check the ADA flag: Read the ADA 1:12 flag. Yes means the ramp is at or below the ADA maximum. No means the ramp is too steep for a public wheelchair ramp.

A homeowner designing a wheelchair ramp to a 24 inch porch picks 'Find Required Ramp Length', enters 24 for the rise, and leaves the target ratio at 12. The calculator returns 24 ft of run, an 8.33 percent grade, a 4.76 degree angle, and an ADA flag of Yes, so they order lumber for a 24 ft run.

A ladder leaning against a wall uses a similar 4:1 ratio safety rule, and the Ladder Angle Calculator applies the same rise over run conversion to set a safe leaning angle.

The result panel writes the ramp slope in the three units a builder, an inspector, and an angle gauge all use, so the same calculation is enough for design, code check, and field layout.

• • Three slope units in one view: Returns the ramp slope as a 1:N ratio, a percent grade, and an angle in degrees from the same rise and run pair.
• • Built-in ADA 1:12 check: Flags the result as Yes or No against the ADA 1:12 maximum for new public wheelchair ramps.
• • Length mode for new ramps: Switches to a length mode that sizes the required run from a rise and a target ratio, so a 30 inch rise at 1:12 returns 30 ft of run.
• • Gentle to steep presets: Supports the 1:20 walkway, 1:15 gentle, 1:12 ADA, 1:10 residential, and 1:8 equipment ratios.
• • Real-time recalculation: Updates the result panel as soon as any rise, run, or ratio field changes.

The result is reproducible because the formula is the same rise-over-run division in either mode, and the ADA flag is set by the same 1:12 threshold.

When the slope angle needs to be transferred to a circular saw for a bevel cut on the ramp's side stringer, the Angle Cut Calculator takes the same arctangent result and returns the miter and bevel angles.

A few site and design factors shift the actual ramp slope away from the theoretical value, and the ADA flag should always be re-checked against the final layout.

• • The calculator handles a single straight ramp run. Switchback and L-shaped ramps need one calculation per straight run, plus a flat landing between them.
• • The ADA flag uses the federal 1:12 maximum. Local jurisdictions may require shallower ramps, so confirm the result with the local building department before pouring or framing.
• • The result is rounded for display only. Internal values use the full double-precision division, so chained calculations should use the unrounded rise-over-run result.

The percent grade is the same percent used in drainage and driveway work, and the angle in degrees is the same angle an angle gauge reads on the framing square.

According to ADA 2010 Standards, the maximum slope of a wheelchair ramp in new construction shall be 1:12, meaning 1 inch of rise for every 12 inches of run, with a maximum rise of 30 inches per run.

According to the US Access Board, every ramp run must end on a 60 inch level landing on a firm, stable, slip-resistant surface, so finished surface thickness has to be measured before the slope is checked.

For a tight lot where a 24 ft ramp does not fit, the Stair Calculator sizes a step layout for the same vertical rise, including tread depth, riser height, and code-compliant landings.