Ramp Slope Calculator
The ramp slope calculator finds a ramp’s slope from its rise and run, or the length of ramp a step or threshold needs at the steepest slope you are allowed. Results come as a percentage, a 1:n ratio and an angle, with long rises split into runs and landings by the figures you enter.
Ramp slope calculator
Planning aid, not a building-code check. Requirements vary by jurisdiction and building type. Confirm with your local rules or a qualified professional. Handrails, edge protection, surface, width and turning spaces are not checked.
Bare numbers are meters; 190 mm works too.
Leave blank to skip the concrete volume.
Assumptions
Change any value to match your product or local rules.
Basis: Example only. Ramp limits differ by country, building type and use; enter the figures from your local accessibility rules
Leave blank (or 0) for no limit.
Basis: Example only. Ramp limits differ by country, building type and use; enter the figures from your local accessibility rules
Leave blank (or 0) for none.
Basis: Example only. Ramp limits differ by country, building type and use; enter the figures from your local accessibility rules
- Slope (%)
- 8.33 %
- Slope (1:n)
- 1:12
- Angle
- 4.76°
- Run (horizontal)
- 5.40 m
- 17′ 9″
- Length along the ramp surface
- 5.42 m
- 17′ 9″
- Runs and landings
- 1 run, no intermediate landing
- Total length with landings
- 5.40 m
- 17′ 9″
- Against your maximum
- Within your maximum 1:12 (8.33 %)
- Concrete volume
- Enter the ramp width to see the concrete volume.
A rise of 0.45 m (1′ 6″) at 1:12 (8.33 %, 4.76°) needs 5.40 m (17′ 9″) of horizontal run.
How this was calculated
- Slope % = rise ÷ run × 100; ratio 1:n with n = run ÷ rise; angle = atan(rise ÷ run)
- Run for a slope 1:n = rise × n
- Surface length = √(rise² + run²)
- Runs = rise ÷ maximum rise per run, rounded up; landings between runs = runs − 1
- Total length = run + landings × landing length
- Concrete, one run only: solid wedge = ½ × rise × run × width; slab = surface length × width × thickness (landings not included)
- Run = 0.45 m × 12 = 5.40 m
- Slope = 0.45 m ÷ 5.40 m × 100 = 8.33 %
- Angle = atan(0.08) = 4.76°
- Surface length = √((0.45 m)² + (5.40 m)²) = 5.42 m
- Runs = 0.45 m ÷ 0.75 m, rounded up = 1
- Total length = 5.40 m + 0 × 1.50 m = 5.40 m
How it works
Pick what you know
Rise and run to get the slope; rise and your maximum slope to get the length; or rise and a slope you type in %, 1:n or degrees.
Slope three ways
Percent = rise ÷ run × 100. The ratio 1:n has n = run ÷ rise. The angle is atan(rise ÷ run).
Length for a rise
At a slope of 1:n the run is rise × n. The length along the sloping surface is √(rise² + run²), a little longer.
Runs and landings
If you enter a maximum rise per run, the rise is split into equal runs with a landing of your length between each pair.
Worked example
A 450 mm rise at 1:12 needs 450 × 12 = 5400 mm of horizontal run. That is a slope of 8.33 % and an angle of 4.76°, and the sloping surface is √(450² + 5400²) ≈ 5419 mm long. With the example limit of 750 mm rise per run, 450 mm fits in one run with no intermediate landing.
In imperial, an 18 in rise at 1:12 needs 216 in, or 18 ft, of run at the same 4.76°.
Slope as a percentage, ratio and angle
| Percent | Angle | |
|---|---|---|
| 1:8 | 12.5 % | 7.13° |
| 1:10 | 10 % | 5.71° |
| 1:12 | 8.33 % | 4.76° |
| 1:15 | 6.67 % | 3.81° |
| 1:20 | 5 % | 2.86° |
Landings and long ramps
Building rules may limit how much a single run of ramp rises before a level landing, and set the landing length. Those figures differ by country, building type and use, so the calculator starts with example values and asks for yours. Leave the maximum rise per run blank (or 0) to treat the ramp as one run.
The total length adds the intermediate landings to the horizontal run. Top and bottom landings are not included; add them from your own rules when you mark out the space.
Measuring the rise correctly
Measure the rise vertically, from the finished surface where the ramp starts to the finished surface where it ends; if the ground slopes away, the rise is more than the step height. On uneven ground, use a level and a straight edge laid toward where the ramp will start, and measure at that point.
The run is horizontal distance on plan, which is what you can mark out on the ground. Slope is measured against it, and the ramp surface length is shown separately.
Concrete for a ramp
Enter the ramp width to see the concrete volume. A solid ramp is a wedge: ½ × rise × run × width. A slab laid on a sloped, compacted base is surface length × width × thickness. A 450 mm rise at 1:12 and 1.2 m wide is ½ × 0.45 × 5.4 × 1.2 = 1.458 m³ solid, or 5.419 × 1.2 × 0.1 ≈ 0.650 m³ as a 100 mm slab. In imperial, a 24 in rise at 1:12 and 48 in wide is 96 cu ft (about 3.56 cu yd) solid, or about 32.1 cu ft (1.19 cu yd) as a 4 in slab.
The volume is shown for a ramp of one run only, and landings, footings and kerbs are not included: work out each run and landing separately and add them. The result links to the concrete mix calculator with the volume filled in, for cement, sand and aggregate.
Pet, vehicle and forklift ramps
The calculator works for any ramp: it only turns a rise and a slope into a length, or a rise and a run into a slope. What changes from one use to another is the steepest slope that is safe, and that figure has to come from someone who knows the user, the vehicle or the truck.
For a pet or bed ramp, use the “Slope as an angle” example and type the angle your vet or the ramp maker suggests. We found no veterinary source that gives one angle for every dog, so the 20° in the example is only a starting value to change.
For a forklift ramp, check the slope against the truck maker’s maximum grade for that model, given in its operator’s manual. In the US, OSHA’s rule for powered industrial trucks (29 CFR 1910.178(n)(7)) sets no maximum grade: it says grades are to be climbed and descended slowly, and on grades over 10 percent a loaded truck is driven with the load upgrade.
For a car ramp or driveway, compare the slope with the vehicle’s approach and departure angles and with your local driveway and parking rules, which differ from place to place.
UK and Australian ramp gradients
| Maximum gradient | Maximum rise of the flight | Source | |
|---|---|---|---|
| England, flight going 10 m | 1:20 | 500 mm | Approved Document M, Vol. 2, Table 1 |
| England, flight going 5 m | 1:15 | 333 mm | Approved Document M, Vol. 2, Table 1 |
| England, flight going 2 m | 1:12 | 166 mm | Approved Document M, Vol. 2, Table 1 |
| Australia, ramp at an external door or inside a house | 1:8 | Not stated | NCC 2022 Housing Provisions, 11.2.3 |
| Australia, required exit ramp that is not an accessible ramp | 1:8 | Not stated | NCC 2022 Volume One, D3D11 |
Where these figures come from
England: the first three rows are Table 1, “Limits for ramp gradients”, in Approved Document M, Volume 2 (buildings other than dwellings), 2015 edition with the 2020 and 2024 amendments. Its note allows the gradient to be interpolated for goings between 2 m and 10 m, for example 1:14 for a 4 m going. Paragraph 1.26 also asks for a surface width of at least 1.5 m, a landing of at least 1.2 m at the foot and head, and intermediate landings of at least 1.5 m. For new homes, Approved Document M, Volume 1 (2015 edition incorporating 2016 amendments) sets a gradient between 1:20 and 1:12 for an accessible and adaptable dwelling, M4(2), and between 1:20 and 1:15 for a wheelchair user dwelling, M4(3). Wales, Scotland and Northern Ireland have their own documents.
Australia: the National Construction Code 2022 Housing Provisions, clause 11.2.3, says a ramp serving an external doorway or inside a building must be no steeper than 1:8. NCC 2022 Volume One, clause D3D11, also gives 1:8 for a ramp that is a required exit, unless it is an accessible ramp, which must follow AS 1428.1; clause D4D12 limits a series of connected ramps on an accessway to a combined rise of 3.6 m. We could not read AS 1428.1 itself, which is sold by Standards Australia, so its ramp gradients are not listed here. Check which edition of the NCC your state has adopted.
To use a row, enter its gradient as the maximum slope and its maximum rise as the rise per run. The calculator shows the arithmetic only. It does not check width, landings, handrails, kerbs or surfaces, and a result “within your maximum” is not proof that a ramp complies; a building control body or certifier decides that.
Frequently asked questions
How do I calculate ramp slope?
Divide the rise by the horizontal run. 450 mm over 5400 mm is 0.0833: a slope of 8.33 %, a ratio of 1:12 (5400 ÷ 450) and an angle of atan(0.0833) ≈ 4.76°.
How long does a ramp need to be for a given rise?
Multiply the rise by n of the steepest slope you may use. At 1:12, a 300 mm rise needs 3600 mm of run and a 24 in rise needs 24 ft. Add landings if the rise is more than your rules allow in one run.
What is 1:12 as a percentage and angle?
1 ÷ 12 = 8.33 %, and atan(1 ÷ 12) ≈ 4.76°. In the other direction, a 5 % slope is 1:20 and a 5° slope is about 1:11.4.
Is slope measured along the ramp or horizontally?
Horizontally. Slope is rise over horizontal run. The length along the ramp surface is a little longer and is shown separately, because it is what you need when ordering a ramp or its edging.
When do I need a landing?
Your local rules decide, as a maximum rise or length per run. Enter that figure and the landing length, and the calculator splits the ramp into equal runs with landings between them.
Ready to plan your space?
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