Match your recipe goal: for creamy mash, prioritize starchy swaps (russet); for shape-holding roasts, prioritize waxier swaps (red or baby gold).
Use the listed substitution ratio by weight (1:1 most swaps).
Adjust cooking time: starchy potatoes often soften faster inside; waxier potatoes hold firm longer and may need a few extra minutes to brown.
For mashed or baked results, manage moisture—start with less added butter/milk/cream than usual if your swap is drier (like russet).
Taste and texture-check at the end: mash until smooth for creaminess, or roast until edges crisp for golden bite.