What size RIB do I need?

Short answer. Start from how many people go out on a normal weekend, then add the gear they bring, then let that number point you to a length. Do not start from length.

01 · Count the people, not the boat

Most buyers open a search by typing a length in feet. That backs the decision in from the wrong end. The number that actually matters is how many people are aboard on a typical outing, and specifically how many need to sit comfortably at speed, not just fit at anchor.

02 · What travels with them

Watersports gear, a cooler, dive tanks, folding chairs: all of it competes with people for inside beam and deck space. A boat sized correctly for four adults with no gear will feel small for four adults with a ski, a wakeboard, and a cooler for the day.

03 · Working through an example

The ADB 420 has an inside width of 1.08 m (3 ft 6.5 in) between the tubes, enough that four adults can sit without anyone perched on a tube, and a CE persons rating of seven. That gap between the comfortable number and the certified number is normal and is exactly the gap this article is about: size for the four you actually take most weekends, and treat the higher rated capacity as a legal ceiling, not a planning target.