Tool
How many steps that door actually wants
A 4-step stair under a low door is not safer. It is a stack of short, annoying risers. Start with the threshold height, then match a product.
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3-tread stair
3 treads4 equal risers at 7 inches. Suggested tread depth is 11 inches, from the old 2×riser + tread ≈ 25 rule, held between 8.5 and 11. The run is about 33 inches.
Three treads match a 3-step portable stair. Compare the assembled height with the threshold on level pavement, both hitched and unhitched if this is a trailer.
The assumptions, in the open
- Risers are equal. A stair with a surprise tall last step is the one people trip on.
- Suggested tread depth comes from 25 minus twice the riser, then clamped between 8.5 and 11 inches. That is a comfort guide, not the International Residential Code applied to an RV.
- Minimum riser in the math is 6 inches. Shorter than that and you are shuffling.
- Product names like "3-step" are tread counts. Confirm the assembled height. Makers do not all publish it.
- A handrail belongs on anything taller than one tread. The calculator does not remove that.
The step roundup splits doorway steps from portable stairs. If the step you have already wobbles, tightening it is a different job from buying a taller one.
Questions worth answering first
Why is the tread count one less than the riser count?
The default assumes a freestanding stair whose top tread is still below the doorway. You step on each tread, then up into the RV. That last move is a riser without its own tread. Switch the toggle if your stair lands level with the floor, the way a doorway-mounted step often does.
What riser is comfortable?
We start at 7.75 inches, the usual maximum for a house stair, and we treat that as comfort rather than a rule RVs have to meet. The default cap is 8.5 inches. Lippert's Solid Step 4.0 listing uses an 8-inch rise. DNYKER prints an 8.9-inch tread depth, which is a bit shallow next to the 2×riser + tread ≈ 25 guide.
Where do I measure?
On level pavement, from the ground to the top of the threshold, at the door you will use. Measure a trailer hitched and unhitched. The number that matters is the one you will live with at the site, which is usually unhitched.