Length of Slope Calculator
When a ramp, roof or hillside trail climbs as it travels, the distance along its surface is longer than the flat distance on a plan, and ordering materials from the flat number leaves you short. This calculator takes the horizontal distance and the elevation change, in feet, and returns that true slope length with the Pythagorean theorem: nothing more, and stated that plainly.
Length of Slope (feet)
Quick Answer
For the pre-filled ramp, a 24 ft horizontal distance with a 2 ft elevation change, the length of slope is 24.08 ft: the square root of (24² + 2²) = √580. That is the 1:12 ramp proportions used for accessible entrances, and the surface you build is only about an inch longer than the flat run. Steeper slopes stretch the gap fast, which the verified runs table below shows.
Key takeaways
- Slope length is the hypotenuse: √(run² + rise²). It is the length you measure with a tape laid on the surface, and the length to order material against.
- This calculator works in feet only, and says so on its fields and its result. That honesty matters, because the same number in meters would be silently mislabeled here.
- Signs do not matter and zero rise is fine: the formula squares both inputs, so a downhill slope and a flat run both return sensible lengths.
- It does not return angle or grade. Those formulas are printed on this page for hand use, but any page claiming this tool computes them is describing a different tool.
- Quick Answer
- How to use the length of slope calculator
- The formula: one right triangle, three sides
- Worked example: the 1:12 accessible ramp, plus five checked runs
- Where the true slope length earns its keep
- What this calculator does not do, stated plainly
- What competing calculators miss
- Length of slope is not length of pull
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use the length of slope calculator
Two measurements in, one length out. The only real way to get a wrong answer is to mix units or measure the run along the slope instead of flat.
- Horizontal distance (run): the flat distance from the bottom of the slope to the point directly beneath its top, in feet. On a plan or map, this is the number you already have. It is not the distance walked up the slope.
- Elevation change (rise): the vertical difference between the bottom and the top, in feet. A level and a tape, a laser measure, or site elevations from a survey all give you this.
- Calculate: the result appears in feet to two decimal places, in the format the tool has always used, for example 24.08 ft. Blank or non-numeric fields return the message Please enter valid numbers in the same box.
- Copy or share: the buttons under the result copy a plain-text summary with both inputs and the slope length, handy for a materials list or a message to a contractor.
Schematic, not to scale: the pre-filled ramp rises only 2 ft over 24 ft, so a true-scale drawing would look almost flat.
The formula: one right triangle, three sides
The run and the rise meet at a right angle, so the slope surface is the hypotenuse of a right triangle and the Pythagorean theorem gives its length directly. The MathWorld statement of the Pythagorean theorem is the whole of the mathematics here; there is no hidden second formula.
Worked: √(24² + 2²) = √(576 + 4) = √580 = 24.08 ft
Not computed by this tool, for hand use: slope angle = arctan(rise ÷ run); grade percent = (rise ÷ run) × 100
Two consequences of the squaring are worth knowing before you trust an input. First, the result can never be shorter than the longer of your two inputs, so a slope length smaller than your run means a typo, not a discovery. Second, signs vanish: a surveyed elevation change of -2 ft and a rise of 2 ft produce the same 24.08 ft on a 24 ft run, which is correct for length but means the tool will never catch a sign error for you.
Worked example: the 1:12 accessible ramp, plus five checked runs
An entrance sits 2 ft above the ground outside it. At the 1:12 maximum running slope in the U.S. Access Board’s ADA guide to accessible routes, each foot of rise needs 12 ft of run, so the ramp runs 24 ft horizontally. Enter 24 and 2 and the calculator returns 24.08 ft of actual ramp surface: the number to build and order against, and the fields above are pre-filled with exactly this run.
Five more runs, each produced by the calculator above and checked against the formula by hand:
| Horizontal distance | Elevation change | Length of slope | Where it shows up |
|---|---|---|---|
| 8 ft | 2 ft | 8.25 ft | A short garden ramp or loading step |
| 3 ft | 4 ft | 5.00 ft | The classic 3-4-5 triangle, exact |
| 30 ft | 40 ft | 50.00 ft | The same triangle scaled by ten, exact |
| 10 ft | 0 ft | 10.00 ft | Dead flat: slope length equals the run |
| 1.5 ft | 2.5 ft | 2.92 ft | A fractional run, rounded to two decimals |
Where the true slope length earns its keep
The slope length is the ordering number and the walking number; the run is the planning number. Confusing the two under-orders material on anything steep.
- Ramps and accessibility work: the ramp surface, its handrails and its edge protection all follow the sloped length, not the footprint. On gentle 1:12 work the difference is about an inch over 24 ft; on a steep equipment ramp it is feet.
- Stairs: total run and total rise give the stringer length directly. For sloped ground under a deck, the deck slope calculator covers the deck-specific steepness questions this tool does not.
- Roofs and drainage: rafter and membrane lengths are slope lengths. The fall itself is a separate question: a concrete slope calculator handles drainage falls in poured work, and a gutter slope calculator handles the shallow falls gutters need.
- Land and trails: a hillside path walks longer than its map distance. For the steepness of the terrain itself rather than one surface, the land slope calculator is the closer tool; this one answers how long the surface is once you know the run and the climb.
What this calculator does not do, stated plainly
It returns one number, in feet, for a straight slope. Four limits follow from that, and each one has sent a reader of the old page away with a wrong expectation:
- Feet only. The old page’s FAQ said inches or meters were fine as long as they were consistent. The arithmetic tolerates that, but the result is labeled in feet and the suffix ft is hard-coded, so a meter run returns a meter number mislabeled as feet. Convert first.
- No angle, no grade, no ratio. Rivals bundle these in; this tool does not compute them. The hand formulas are in the formula box above, and nothing on this page claims the tool produces them.
- Straight slopes only. A curved hillside path, a switchback trail or a multi-pitch roof has no single run and rise. Break it into straight sections and run each one.
- Length, not area or volume. To order a surface material you still need the width: area is slope length times width, and this tool stops at the length.
What competing calculators miss
The formula is public domain and every rival gets it right, so the competition is about everything around the number: units, extra outputs and honest scoping.
- Brave Calculator’s length of slope page: the same formula and a sound 3 ft rise over 36 ft example (36.12 ft), but it stops at the single number with no worked checks, no negative or zero input behaviour, and no statement of what the tool will not do. This page publishes all three.
- MiniWebTool’s slope and grade calculator: broader, with modes for percent, ratio and angle and several units, but the breadth buries the one question this keyword asks, and its length output sits three clicks into a mode picker. Here the length is the whole tool, one click deep.
- Omni Calculator’s slope family: polished and multi-unit, spread across separate slope, rise-over-run and elevation-grade pages, so the hypotenuse is a by-product inside tools aimed at steepness. A reader who only needs a surface length wades through grade theory to find it.
- Ramp specialists (CalcSummit, OnlyCalculators): genuinely strong on accessibility work, with ADA landings, handrail rules and cost estimates, but they answer a ramp-design question. For a stair stringer, a roof plane or a hillside path, their framing misleads as often as it helps.
- The gap this page fills: the single-purpose length, in feet, with a pre-filled ADA-proportioned example, five more verified runs including the exact 3-4-5 checks, the zero and negative behaviours demonstrated, and the feet-only limit disclosed instead of papered over.
Length of slope is not length of pull
The names collide in search results, so the distinction belongs on the page. Length of slope is this measurement: the diagonal surface length of a ramp, roof or hillside, computed from a horizontal run and a vertical rise. Length of pull is a firearm measurement, the distance from a rifle or shotgun trigger to the end of its buttstock, used to fit a stock to a shooter’s arm. No input overlaps, no formula overlaps, and neither tool can stand in for the other. If your problem involves a trigger rather than a triangle, you want the gun-fit calculator, not this one.
Frequently asked questions
It is the actual distance measured along the sloped surface, from bottom to top. That surface is the hypotenuse of a right triangle whose other two sides are the horizontal distance (the run) and the elevation change (the rise), so the slope length is always at least as long as the run and longer whenever there is any rise at all.
The Pythagorean theorem: length of slope = square root of (run squared + rise squared). For the pre-filled ramp example, that is the square root of (24 squared + 2 squared) = the square root of 580 = 24.08 ft. Both inputs must be in the same unit, and this calculator works in feet.
The arithmetic would still work, because the formula only needs both inputs in the same unit, but this calculator labels its fields and its result in feet and always appends ft to the answer. A result computed from meter inputs would be a meter value wearing a feet label, so convert to feet first and read the answer as feet.
Nothing changes. The formula squares both inputs, so a rise of -2 ft returns exactly the same length as a rise of 2 ft, and a downward slope has the same surface length as an upward slope with the same run and elevation change. The tool accepts negative entries without a warning, which is worth knowing if a sign error ever slips into your measurements.
The slope length equals the horizontal distance exactly, because there is no incline: the square root of (run squared + 0) is the run itself. Both inputs at zero are also accepted and return 0.00 ft. Leaving either field blank, or typing text, is the only input state that produces the Please enter valid numbers message.
No. It returns the slope length only. The angle is arctan(rise divided by run) and the grade is (rise divided by run) times 100, and this page shows both formulas in the formula section so you can work them out by hand, but the tool itself does not compute them and this page will not pretend otherwise.
Yes, for any straight slope. For stairs, enter the total horizontal depth of the flight as the run and the total floor-to-floor height as the rise, and the result is the stringer length before you add nosing and trim allowances. For a ramp it gives the surface length to order and build. For a curved or multi-pitch slope it does not apply: each straight section needs its own run.
No. Length of slope is a construction measurement: the diagonal of a rise-and-run triangle. Length of pull is a firearm stock measurement, the distance from a trigger to the end of a buttstock, estimated from a shooter’s arm. They share the word length and nothing else, and neither calculator can do the other’s job.
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References
- Weisstein, E. W., MathWorld (Wolfram). Pythagorean Theorem. Accessed October 22, 2026.
- Weisstein, E. W., MathWorld (Wolfram). Right Triangle. Accessed October 22, 2026.
- Encyclopaedia Britannica. Pythagorean Theorem. Accessed October 22, 2026.
- U.S. Access Board. ADA Guides, Chapter 4: Accessible Routes (Ramps). Accessed October 22, 2026.
- U.S. Department of Justice. 2010 ADA Standards for Accessible Design, Section 405: Ramps. Accessed October 22, 2026.
- National Institute of Standards and Technology. SI Units: Length. Accessed October 22, 2026.