Calculator
Example data table
| Scenario | Rise (in) | Run (in) | Ratio (1:x) | Slope (%) | Angle (°) | Notes |
|---|---|---|---|---|---|---|
| Garden step bypass | 6 | 72 | 1:12 | 8.33 | 4.76 | Compact solution, add texture for grip. |
| Deck access | 18 | 360 | 1:20 | 5.00 | 2.86 | Gentle slope, good for frequent use. |
| Tool shed threshold | 3 | 48 | 1:16 | 6.25 | 3.58 | Short ramp; ensure edges are protected. |
Formula used
- Slope ratio:
run / rise(displayed as1 : (run/rise)). - Slope percent:
(rise / run) × 100. - Ramp length (sloped):
√(rise² + run²). - Angle:
atan(rise/run), converted to degrees. - Required run for a target ratio:
rise × target_ratio. - Run splitting:
runs_needed = ceil(rise / max_rise_per_run).
How to use this calculator
- Select your unit system, then enter the vertical rise.
- Enter either horizontal run or ramp length; you can enter both if consistent.
- Pick a slope limit to compare against, or set a custom ratio.
- Set max rise per run and landing length to estimate how many runs you need.
- Press Calculate to view results above the form.
- Use the download buttons to export a summary for your project notes.
Professional notes
Slope targets for garden access
Most mobility users experience a steepness change before they notice length. A 1:12 limit equals an 8.33% grade, while a 1:20 target equals 5.00%. In gardens, the gentler option reduces slipping risk when surfaces are damp from irrigation, shade, or moss growth.
Translating rise into footprint
Horizontal run is the space the ramp consumes on the ground. This calculator converts your rise to the run required for a chosen ratio using run = rise × ratio. For example, a 24 inch rise needs 288 inches of run at 1:12, and 480 inches at 1:20. Use this to confirm the ramp will fit between beds, fences, and gates. Add clearance so wheelbarrows and chairs can align.
Run splitting and landings
Long ramps feel safer when separated into shorter runs with level landings. The tool estimates runs using runs_needed = ceil(rise ÷ max rise per run). When rise exceeds the limit, additional landings reduce fatigue and provide stopping points for wheelchairs, carts, and walkers. The footprint estimate adds landing length for intermediate and optional top and bottom landings. Keep landings level to avoid rolling and to ease turning.
Surface, drainage, and edging
Outdoor ramps should manage water and traction. Textured concrete, broom finishes, or composite surfaces with grit inserts improve grip. Cross-slope should remain minimal so wheels do not drift sideways. Provide edge protection, planting set-backs, and drainage breaks so runoff does not sheet across the ramp during rain or hose watering. In planting zones, control soil spillover with curbs or boards. In icy climates, plan for de-icing storage and meltwater flow.
Interpreting the results responsibly
The ratio, percent, and angle describe the same slope from different viewpoints. Use percent for landscape grading discussions and ratio for accessibility checks. If results show “slope steep,” increase run or reduce rise by re-grading. Always verify local requirements, handrail triggers, and turning clearances before construction. Measure heights after preparation, because pavers and settlement can change rise over time.
FAQs
What does “1:12” mean?
It means for every 1 unit of rise, the ramp needs 12 units of horizontal run. A 12 inch rise needs 144 inches of run.
Which input is best: run or ramp length?
Use run when you are checking available ground space. Use ramp length when you measured the sloped surface. Entering both is fine if they match the same right triangle.
Why does the calculator suggest multiple runs?
If rise exceeds the max rise per run setting, the ramp is split into shorter runs with landings. This reduces effort, creates resting points, and improves control on outdoor paths.
How are landings counted in the footprint?
Intermediate landings are added between runs. You can also include top and bottom landings. The calculator adds landing length to the total run to estimate the required ground footprint.
Can I use metric values?
Yes. Select Metric and enter dimensions in millimeters. The tool converts internally and reports results in millimeters, plus area in square meters.
Does this replace code compliance checks?
No. It is a planning calculator. Always confirm local rules for handrails, clear widths, edge protection, turning space, and surface requirements before building.