If you're choosing a narrow urban bench for a busy sidewalk, the narrowest two-person option that still feels comfortable is about 44–48 inches wide (112–122 cm) overall. That gives each adult roughly 22–24 inches of hip room and enough space for coats or bags without pressing shoulders together. Below 42 inches, two people can technically sit, but they usually perch at the edges or one person avoids the bench entirely.
For busy sidewalk seating, a compact outdoor bench usually works better than a full-size park bench. Width is only part of the equation: choose a backless or slim-back design that can sit against a building line, planter edge, or low wall. A seat depth of 16–18 inches works for short sits and keeps the profile compact; 18–22 inches is better if you expect people to wait, drink coffee, or rest longer. Keep seat height around 17–19 inches so it is easy to get up from, and avoid wide armrests or a center divider—they steal seating space on an already compact bench.
The key bench dimensions are width, depth, height, and clear passage in front. Pedestrian flow matters as much as bench size. Mount the bench parallel to the building or curb line, and leave at least 5 feet of clear walkway in front of it; on a busy commercial sidewalk, 6–8 feet is safer. Open legs and a visually light frame will also help the bench feel less bulky and keep sightlines open.
A practical specification is 48 inches long × 18 inches deep × 18 inches high, backless, fixed parallel to the storefront. That is narrow enough for a busy sidewalk but still gives two adults a decent place to sit without getting in the way.