Select the substitute based on the dish type: raspberries or frozen mixed berries for baking; blueberries, figs, or grapes for fresh dishes.
Measure the substitute at a 1:1 volume ratio to blackberries, adjusting for chopped figs or grapes as needed.
If needed, drain or chop the substitute to match texture and moisture of blackberries.
For sweeter substitutes like blueberries, figs, or grapes, add a teaspoon of lemon juice per cup to enhance tartness.
Check final taste and texture, adjusting sweetness or acidity to suit the recipe.