Most porch swing mistakes are measuring mistakes. Three numbers decide whether it hangs right.
1. Width of the porch
Swings come in 4, 5, and 6 foot widths. As a rule of thumb: 4 ft sits two people, 5 ft sits two comfortably, 6 ft sits three. Leave about a foot of clearance on each side, and check that a door or rail does not swing into that arc.
2. Height off the floor
Most adults are comfortable when the seat sits 17 to 19 inches off the porch floor, with 4 to 6 inches of clearance behind the swing so it can move without touching the wall.
3. What it hangs from
Swings ship with chains, but not always with hanging hardware. You need a beam or joist overhead — not a railing — and hooks rated for the load. If the listing shows a weight capacity, keep the total under it: people add up fast on a three-seater.
Hanging the chain
Hang the back chain one link shorter than the front. The seat tilts back slightly, which most people find comfortable and it keeps you from sliding forward.