Identify your dish type: roasting (needs firm pieces), mashing/purée (needs creamy texture), or soups/stews (needs tender chunks).
Choose the closest texture match from the table below and use the listed 1:1 ratio for turnip by weight.
If your substitute is sweeter (rutabaga/parsnip), balance with salt, pepper, and an acid (lemon or vinegar) if the recipe allows.
If your substitute is wetter/firmer than turnip (daikon/celeriac), cut smaller and start checking for tenderness 3–5 minutes earlier.
Taste at the end and adjust: add salt for bland swaps or a small splash of acid to brighten earthy alternatives.