Ramp Calculator uses rise and planned run to calculate slope ratio, required run, surface length, pitch angle and grade. Formula: slope ratio = run ÷ rise, with ADA 1:12 slope status shown.
The Measurement Mistake That Fails Ramp Inspections
Builders often measure the sloped surface length of a ramp and call that the “run.” That single error makes the ramp steeper than the numbers suggest — and it’s the reason many ramps fail a building inspector’s tape measure check. The horizontal run is what governs slope, not the inclined length. This calculator keeps that distinction clean, checking your planned run against the target ratio and flagging exactly where you’re short.
What the Tool Actually Checks
The core formula is dead simple: slope ratio = horizontal run ÷ vertical rise. A 24-inch rise with a 288-inch horizontal run gives 288 ÷ 24 = 12, written as 1:12. The tool takes your rise and your planned run, then compares that actual ratio to whichever target you’ve selected — 1:12 for ADA public ramps, 1:10 for residential, 1:8 for utility or shed access, and 1:4 for equipment loading.
It also does three derivative calculations automatically. The required horizontal run multiplies your rise by the target ratio — that’s the absolute minimum horizontal distance to hit the slope, no margin. The surface length (hypotenuse) tells you how much material you’ll actually need if you build at your planned run. The pitch angle and grade percentage give you the same information in degrees and percent for contractors who think in those units.
Unit handling is straightforward. Switching between US Customary and Metric changes the labels from inches/feet to centimeters/meters, but it does not convert any numbers. If you typed 24 inches and flip to metric, the field still reads 24 — now interpreted as 24 centimeters. You’re expected to re-enter the values in the new unit system manually. The math stays identical regardless of unit; only the display changes.
A Real Build: Deck Ramp to 30-Inch Door Threshold
You’re adding a ramp to a back deck with a 30-inch rise from grade to the door sill. Local code permits a residential 1:10 slope. Enter US Customary, select “Residential / Private Ramp (1:10).” Rise: 30 in. For your first attempt, you measure the available yard length and plan 280 inches of horizontal run.
Hit calculate. The hero output shows 1 : 9.3 — too steep. Required run pops up as 300.0 inches. Your planned surface length would be about 281.6 inches, but the slope fails the 1:10 target. The insight turns to a warning. You now know you need an extra 20 inches of horizontal space. Adjust the run to 300, and the display flips to 1 : 10.0 with a green “Residential Slope Pass.” Surface length becomes roughly 301.5 inches, angle a mild 5.71°, and grade right at 10%.
If this were a public ADA ramp with the same rise, the required run would jump to 360 inches — 30 feet. That’s the reality check this calculator delivers before you pour footings.
The “Planned Horizontal Run” Trap
Here’s where jobs go sideways. The calculator asks for horizontal run, not the length of the ramp boards. If you measure the slope face itself and plug that number in, you’ve oversold the gentleness of the ramp. The tool will cheerfully report a passing slope because it thinks you have more horizontal distance than you actually do.
To see the difference, run a quick comparison: a 24-inch rise with a 288-inch sloped surface (not horizontal). The horizontal run is actually √(288² − 24²) ≈ 287.0 inches. Close in this case, but for steeper ramps the gap widens significantly. Always measure horizontally — from the edge of the landing at the top to the edge of the landing at the bottom, not along the incline. This is the single most common input error and it’s why the tool’s label explicitly says “Planned Horizontal Run.”
Another nuance: the handrail flag only triggers specific rules for the 1:12 ADA target. If your rise exceeds 6 inches (15 cm in metric mode), the card shows “Required.” For all other target ratios — residential, utility, equipment — the handrail status reads “Check Code” regardless of rise, because the tool doesn’t enforce handrail requirements for those non-ADA scenarios. You’ll need to consult local building codes for those applications.
Questions Builders Ask
Why does the tool show “Data Required” when I clear a field?
The calculator rejects any rise or run that is zero, negative, or not a number. If you accidentally leave a field blank or type a dash, the logic sets isValid to false and clears all output displays. Enter positive numbers only.
Does switching from US to metric convert my numbers?
No. Changing the system only updates the unit labels. If you have 24 in the rise field and switch to Metric, it becomes 24 centimeters. You must re-enter the actual metric measurement yourself. The math stays the same.
What’s the difference between required run and planned run?
Required run is the minimum horizontal distance to exactly hit your target slope. It’s rise × target ratio. Planned run is what you type in based on your available space. If planned is shorter than required, you fail. The tool shows both so you can see the gap.
The handrail note says “Not Required” for a 6-inch rise but “Required” for 7 inches. Why?
Per ADA standards, handrails become mandatory when the rise exceeds 6 inches. The tool hard-codes that threshold for the 1:12 target only. For any other target, the handrail field reads “Check Code” because those applications don’t have a universal handrail trigger.
Can I use this to check a ramp that changes direction or has a landing?
No. This calculator works on a single straight run of ramp. If you have a landing and a second segment, treat them separately. The tool doesn’t account for landing dimensions, cross-slope, or overall site layout.