Steps on a slope calculator

Measure the rise and run with stakes, a string and a line level, and divide them into steps as the calculator does. Start at the bottom: dig a level trench for the first tie so its top is one riser above the ground in front, set it, drill ½ in holes about 6 in from its ends and drive #4 rebar through them into the soil, flush with the top. If the steps are boxed, set a side timber (return) at each end, spike it to the tie and pin it with two more bars. Cut the slope behind level, line the bed with non-woven landscape fabric and fill with 3 in of crushed stone to about 1 in below the top of the tie. The next tie goes at the back of that tread, and so on up the slope.

Divide the rise by the height of your timber and round up. With 7 in railroad ties laid flat, a 36 in rise takes 6 steps of 6 in; with 6 × 6 landscape timbers, 5½ in high, it takes 7 steps of 5 1/8 in. The run decides the treads: over 7 ft, six steps give 14 in treads.

Outdoor steps are usually lower and deeper than indoor stairs: a rise of 5½ to 7 in and a tread of 12 to 18 in, with twice the riser plus the tread at about 26 or 27 in (Garden Gate). Keep every riser in a flight the same. For width, 36 in takes one person and about 4 ft is comfortable; go wider where two people will walk side by side.

Each timber reaches below the tread in front of it by its height less the riser — 1 in for 7 in ties with 6 in risers, and nothing at all when the rise divides evenly into whole timbers. That embed keeps the line neat, but it is the rebar that stops a timber kicking out: ½ in (#4) bars about 6 in from each end of every riser and two through each side timber, long enough to go through the timber and 18 in into the soil — 25 in for a railroad tie, 23½ in for a 6 × 6. Firm or rocky ground holds with less; soft fill wants more.

The tread bed is the tread less the timber's depth, times the step width, times the fill depth. With 14 in treads behind 9 in ties that is 5 × 48 × 3 in, about 0.42 cu ft a step — six steps take 2½ cu ft, five 0.5 cu ft bags or about 260 lb of #57 stone. Fill to about 1 in below the top of the timber, so the stone stays on the tread, and tamp it.

The timber caps the riser, so a steep slope shows up as short treads. Once a tread drops under 12 in, or twice the riser plus the tread under 24 in, the steps are too steep to walk comfortably. With 7 in ties that is at most 7 in of rise per 12 in of run — 58% (30°) — when the rise divides into whole 7 in risers; a 3 ft rise needs six 6 in risers and so at least 6 ft of run, 50% or 1 in 2. Steeper than that, angle the path across the slope, add a turn, or terrace the bank with a retaining wall. At the other end, a walk no steeper than 1 in 20 needs no steps at all.

Pressure-treated landscape timbers rated for ground contact are the safer choice. Used railroad ties are treated with creosote, and the EPA says creosote products are not available to homeowners; it notes that creosote-treated ties are sometimes recycled as landscaping timbers, that this reuse is not something it regulates under pesticide laws, and that treated wood should never be burned at home. NMSU Extension goes further: it advises that ties should not be used in landscapes at all and that vegetables should not be grown near them, quoting the EPA that there are no approved uses of creosote to treat wood for residential use. If you use ties anyway, keep them away from food beds and wear gloves and a dust mask when cutting them.

IRC 2021 R311.7 leaves out stairways not within or serving a building, porch or deck, so steps on a garden path are usually outside its stair rules — but your building department has the last word, and steps that lead to a door, a porch or a deck serve it and are a stairway. On house stairs the IRC asks for a handrail on four or more risers (R311.7.8); outdoors one is worth fitting too, especially where the steps are steep or used in the dark.