Those 3 meters in the bottom right are what you need to fill to recruit raiders. You fill those by have sim settlement commercial, agricultural, and industrial plots being worked by your civilians, slaves, vassal settlements (settlements you don't manage but control through fear with your raider patrols and guards) or changing the role of some of your raiders to 'worker' and assigning them to plots (they don't like this, there is a morale penalty).
Those 3 meters in the bottom right are what you need to fill to recruit raiders. You fill those by have sim settlement commercial, agricultural, and industrial plots being worked by your civilians, slaves, vassal settlements (settlements you don't manage but control through fear with your raider patrols and guards) or changing the role of some of your raiders to 'worker' and assigning them to plots (they don't like this, there is a morale penalty).
3 meters is 3.28 yards
p.s. change the role of your raiders by crouching and looking at them you will get a secondary option.