Decide your use case: salad needs crisp bite, wraps need sturdy leaves, and Caesar-style needs thick, chop-friendly texture.
Pick the substitute from the list by texture: iceberg for maximum crunch, butter lettuce for tender-crisp, kale for chewy structure, spinach for tender volume, arugula for peppery punch.
Use the listed ratio; for kale and arugula, cut smaller than you would romaine so the texture spreads evenly.
If the substitute is tougher (kale), massage with a pinch of salt for 30–60 seconds; if it’s tender (spinach), chop small and dress at the last moment.
Taste and adjust: add a little extra salt/acid if your substitute tastes flatter than romaine, or use a creamy dressing to tame arugula pepper.