The short answer is that the smallest practical seated bench for a bus stop is usually about 30–36 inches long, 16–20 inches deep, and 17–19 inches high. In metric terms, that’s roughly 76–91 cm long, 41–51 cm deep, and 43–48 cm high. Once you drop below 30 inches in length, it stops feeling like a shared bench and becomes more of a single seat or perch.
If you need a true one-person bench, some manufacturers offer compact models around 24–30 inches long. That can work on a narrow footpath, but I’d only use it where space is extremely tight. For most bus stops, a 36-inch length is the sweet spot because it gives two adults just enough room without taking over the sidewalk.
There is also a smaller alternative: a leaning rail or perch bench. These can be as narrow as 12–16 inches of width per user and only 8–12 inches deep, since you mostly rest your hips rather than sit fully. The trade-off is comfort and accessibility—older riders or people with mobility issues may struggle with a perch, so many transit agencies still prefer a real seat.
So if you’re specifying a product, the smallest usable off-the-shelf size I’d recommend is around 30–36 in L × 16–20 in D × 17–19 in H, or about 800 mm × 450 mm × 450 mm for a compact metric model. Anything smaller should be treated as a single seat or lean rail, not a full bus stop bench. Check your local transit standards before finalizing the dimensions, because clearance and accessibility rules can force a slightly larger footprint.