Where the length actually goes
Take the defaults: 36 inches of rise at 1 in 12. The run is 432 inches, which is 36 feet, and that is the number people quote. Then the rise gets split, because 36 inches is more than the 30 inches per flight entered here, so it becomes two flights of 18 inches each and 216 inches of run apiece.
Now add the landings. Five feet at the bottom, five feet between the flights, five feet at the top — 180 inches that gains no height at all. The straight-run footprint is 612 inches, or 51 feet, and the landings are 29.4 percent of it. A ramp somebody sketched as thirty-six feet is a fifty-one foot object.
That is the whole reason this page exists. The run is a one-line calculation that any slope calculator does. The landings are what decides whether the ramp fits the site, and they scale with the number of flights rather than with the rise.
The rise-per-flight step function
Flights come from the rise divided by the rise allowed per flight, rounded up, so the footprint jumps rather than growing smoothly. At 30 inches per flight, a 30 inch rise is one flight and 360 inches of run with two landings — 480 inches all in. Push the rise to 31 inches and you get two flights, a third landing, and 372 inches of run: 552 inches all in. One inch of rise added six feet to the footprint.
Which is why it is worth measuring the rise properly before laying anything out, and worth knowing whether a step at the bottom or a bit of regrading can take the total under the threshold. A ramp that needs two flights instead of one is not slightly bigger, it is a different structure.
Switchbacks trade length for width
Folding the run back on itself is the usual answer when the site cannot take fifty feet in a line. The length collapses to roughly one leg plus a landing, and the width becomes two ramp widths side by side plus whatever the turn landing needs. What does not change is the total ramp surface — the same rise at the same slope always needs the same run — so the decking, the framing and the rail footage are what they were. Only the shape of the hole in the site changes.
Rail footage is worth noting on its own. It follows the sloped surface, not the horizontal run, and it picks up extensions at both ends of every flight. Two flights with a foot of extension at each end is four feet of rail per side that is not over any ramp at all.
Why none of the limits are built in
You will notice this page has no opinion about 1 in 12, no maximum rise of its own, and no view on how big a landing has to be. Those figures belong to the standard that governs your particular project, and which standard that is depends on the jurisdiction, the type of building, whether the work is new or an alteration, and sometimes on who is paying for it. They also cover far more than the numbers this page handles: cross slope, level area at a door, what happens where the ramp meets the door swing, edge protection, surface finish, rail height and shape and grip.
So the honest thing a layout calculator can do is divide accurately by whatever you were given and show you the footprint that results, which is the question the site is asking. The compliance question goes to the building department or the authority for the project, before anything gets built.
Adjacent arithmetic: the slope and grade calculator for the same slope in percent, degrees and fall per foot, and the stair stringer calculator for when the answer is stairs instead.
Questions people ask
How long does a ramp need to be for a 36 inch rise?
At 1 in 12 the sloped run is 432 inches, or 36 feet. That is before landings. Split into two flights with five foot landings at the bottom, the middle and the top, the object occupies 612 inches — 51 feet — in a straight line. The run is the easy part of the answer and it is not the part that decides whether the ramp fits.
How much of a ramp footprint is landings?
More than people expect, and it grows with the number of flights rather than with the rise. Two flights with three five-foot landings puts 180 inches of level surface into a 612 inch footprint, which is 29 percent of the length gaining no height. Every extra flight adds another landing and its whole length is dead run.
Does a switchback ramp use less material?
No. The same rise at the same slope always needs the same length of sloped run, so the decking, framing and handrail come out the same. A switchback changes the shape of the footprint, trading a long thin strip for something roughly half as long and twice as wide, plus a turn landing that is usually larger than a straight one.
Is 1 in 12 the required ramp slope?
It is the figure most often quoted, and it is not a rule this page applies. The slope your project is held to comes from the standard your jurisdiction has adopted and from what kind of building it is, and the same standard sets landing sizes, widths, cross slope, edge protection and handrail geometry that a slope number says nothing about. Enter the figure you were given and check the requirements with your building department.
How do I work out handrail length for a ramp?
It follows the sloped surface rather than the horizontal run, so use the hypotenuse of each flight, then add the landings the rail continues across and the extensions at each end of each run. For two 18 inch flights at 1 in 12 that is 216.75 inches of sloped rail per flight rather than 216, plus the landing lengths, plus four extensions.