Identify whether your barberries are used for chew/texture (pilaf, salads, toppings) or mainly for tart flavor (marinades, fillings, quick breads).
Swap using the listed ratio: start at the lower end for strong acids (tamarind, sumac/lemon mixes) and increase only if the flavor feels flat.
If your substitute is dry (cranberries, sour cherries), soak 5-10 minutes to mimic barberry’s plump bite in warm dishes.
If your substitute is liquid-acid based (tamarind, lemon/sumac), add gradually and taste after mixing (before baking/cooking finishes).
Adjust sweetness: barberry is tart, so reduce added sugar or balance with a small pinch of salt when using very tangy swaps.