Match your use case: for hot melting (sandwiches/gratins), prioritize Gruyère/Emmental first; for mild melt, choose Provolone or Mozzarella.
Use the table ratios (generally 1:1). If the substitute is sharper (cheddar) or milder (mozzarella), adjust by slice thickness or a small salt/seasoning tweak.
For baking/gratin-style dishes, grate the cheese so it melts evenly and avoids greasy pockets.
For cold sandwiches, slice thin and let the cheese sit 2–3 minutes to soften slightly for better mouthfeel.
Taste after the first bite and refine: more salt for mild swaps, or balance sharpness with a sweeter component (e.g., caramelized onions).